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Net::SSLeay(3)        User Contributed Perl Documentation       Net::SSLeay(3)




NAME

       Net::SSLeay - Perl extension for using OpenSSL


SYNOPSIS

         use Net::SSLeay qw(get_https post_https sslcat make_headers make_form);

         ($page) = get_https('www.bacus.pt', 443, '/');                 # Case 1

         ($page, $response, %reply_headers)
                = get_https('www.bacus.pt', 443, '/',                   # Case 2
                       make_headers(User-Agent => 'Cryptozilla/5.0b1',
                                    Referer    => 'https://www.bacus.pt'
                       ));

         ($page, $result, %headers) =                                   # Case 2b
                = get_https('www.bacus.pt', 443, '/protected.html',
                     make_headers(Authorization =>
                                  'Basic ' . MIME::Base64::encode("$user:$pass",''))
                     );

         ($page, $response, %reply_headers)
                = post_https('www.bacus.pt', 443, '/foo.cgi', '',       # Case 3
                       make_form(OK   => '1',
                                 name => 'Sampo'
                       ));

         $reply = sslcat($host, $port, $request);                       # Case 4

         ($reply, $err, $server_cert) = sslcat($host, $port, $request); # Case 5

         $Net::SSLeay::trace = 2;  # 0=no debugging, 1=ciphers, 2=trace, 3=dump data

         Net::SSLeay::initialize(); # Initialize ssl library once


DESCRIPTION

       Net::SSLeay module contains perl bindings to openssl
       (<http://www.openssl.org>) library.

       COMPATIBILITY NOTE: Net::SSLeay cannot be built with pre-0.9.3 openssl.
       It is strongly recommended to use at least 0.9.7 (as older versions are
       not tested during development). Some low level API functions may be
       available with certain openssl versions.

       It is compatible with OpenSSL 1.0 and 1.1. Some functions are not
       available under OpenSSL 1.1.

       Net::SSLeay module basically comprise of:

       o   High level functions for accessing web servers (by using
           HTTP/HTTPS)

       o   Low level API (mostly mapped 1:1 to openssl's C functions)

       o   Convenience functions (related to low level API but with more perl
           friendly interface)

       There is also a related module called Net::SSLeay::Handle included in
       this distribution that you might want to use instead. It has its own
       pod documentation.

   High level functions for accessing web servers
       This module offers some high level convenience functions for accessing
       web pages on SSL servers (for symmetry, the same API is offered for
       accessing http servers, too), an "sslcat()" function for writing your
       own clients, and finally access to the SSL api of the SSLeay/OpenSSL
       package so you can write servers or clients for more complicated
       applications.

       For high level functions it is most convenient to import them into your
       main namespace as indicated in the synopsis.

       Basic set of functions

       o   get_https

       o   post_https

       o   put_https

       o   head_https

       o   do_https

       o   sslcat

       o   https_cat

       o   make_form

       o   make_headers

       Case 1 (in SYNOPSIS) demonstrates the typical invocation of get_https()
       to fetch an HTML page from secure server. The first argument provides
       the hostname or IP in dotted decimal notation of the remote server to
       contact. The second argument is the TCP port at the remote end (your
       own port is picked arbitrarily from high numbered ports as usual for
       TCP). The third argument is the URL of the page without the host name
       part. If in doubt consult the HTTP specifications at
       <http://www.w3c.org>.

       Case 2 (in SYNOPSIS) demonstrates full fledged use of "get_https()". As
       can be seen, "get_https()" parses the response and response headers and
       returns them as a list, which can be captured in a hash for later
       reference. Also a fourth argument to "get_https()" is used to insert
       some additional headers in the request. "make_headers()" is a function
       that will convert a list or hash to such headers. By default
       "get_https()" supplies "Host" (to make virtual hosting easy) and
       "Accept" (reportedly needed by IIS) headers.

       Case 2b (in SYNOPSIS) demonstrates how to get a password protected
       page. Refer to the HTTP protocol specifications for further details
       (e.g. RFC-2617).

       Case 3 (in SYNOPSIS) invokes "post_https()" to submit a HTML/CGI form
       to a secure server. The first four arguments are equal to "get_https()"
       (note that the empty string ('') is passed as header argument).  The
       fifth argument is the contents of the form formatted according to CGI
       specification.  Do not post UTF-8 data as content: use utf8::downgrade
       first. In this case the helper function "make_https()" is used to do
       the formatting, but you could pass any string. "post_https()"
       automatically adds "Content-Type" and "Content-Length" headers to the
       request.

       Case 4 (in SYNOPSIS) shows the fundamental "sslcat()" function
       (inspired in spirit by the "netcat" utility :-). It's your swiss army
       knife that allows you to easily contact servers, send some data, and
       then get the response. You are responsible for formatting the data and
       parsing the response - "sslcat()" is just a transport.

       Case 5 (in SYNOPSIS) is a full invocation of "sslcat()" which allows
       the return of errors as well as the server (peer) certificate.

       The $trace global variable can be used to control the verbosity of the
       high level functions. Level 0 guarantees silence, level 1 (the default)
       only emits error messages.

       Alternate versions of high-level API

       o   get_https3

       o   post_https3

       o   put_https3

       o   get_https4

       o   post_https4

       o   put_https4

       The above mentioned functions actually return the response headers as a
       list, which only gets converted to hash upon assignment (this
       assignment looses information if the same header occurs twice, as may
       be the case with cookies). There are also other variants of the
       functions that return unprocessed headers and that return a reference
       to a hash.

         ($page, $response, @headers) = get_https('www.bacus.pt', 443, '/');
         for ($i = 0; $i < $#headers; $i+=2) {
             print "$headers[$i] = " . $headers[$i+1] . "\n";
         }

         ($page, $response, $headers, $server_cert)
           = get_https3('www.bacus.pt', 443, '/');
         print "$headers\n";

         ($page, $response, $headers_ref)
           = get_https4('www.bacus.pt', 443, '/');
         for $k (sort keys %{$headers_ref}) {
             for $v (@{$$headers_ref{$k}}) {
                 print "$k = $v\n";
             }
         }

       All of the above code fragments accomplish the same thing: display all
       values of all headers. The API functions ending in "3" return the
       headers simply as a scalar string and it is up to the application to
       split them up. The functions ending in "4" return a reference to a hash
       of arrays (see perlref and perllol if you are not familiar with complex
       perl data structures). To access a single value of such a header hash
       you would do something like

         print $$headers_ref{COOKIE}[0];

       Variants 3 and 4 also allow you to discover the server certificate in
       case you would like to store or display it, e.g.

         ($p, $resp, $hdrs, $server_cert) = get_https3('www.bacus.pt', 443, '/');
         if (!defined($server_cert) || ($server_cert == 0)) {
             warn "Subject Name: undefined, Issuer  Name: undefined";
         } else {
             warn 'Subject Name: '
                 . Net::SSLeay::X509_NAME_oneline(
                        Net::SSLeay::X509_get_subject_name($server_cert))
                     . 'Issuer  Name: '
                         . Net::SSLeay::X509_NAME_oneline(
                                Net::SSLeay::X509_get_issuer_name($server_cert));
         }

       Beware that this method only allows after the fact verification of the
       certificate: by the time "get_https3()" has returned the https request
       has already been sent to the server, whether you decide to trust it or
       not. To do the verification correctly you must either employ the
       OpenSSL certificate verification framework or use the lower level API
       to first connect and verify the certificate and only then send the http
       data. See the implementation of "ds_https3()" for guidance on how to do
       this.

       Using client certificates

       Secure web communications are encrypted using symmetric crypto keys
       exchanged using encryption based on the certificate of the server.
       Therefore in all SSL connections the server must have a certificate.
       This serves both to authenticate the server to the clients and to
       perform the key exchange.

       Sometimes it is necessary to authenticate the client as well. Two
       options are available: HTTP basic authentication and a client side
       certificate. The basic authentication over HTTPS is actually quite safe
       because HTTPS guarantees that the password will not travel in the
       clear. Never-the-less, problems like easily guessable passwords remain.
       The client certificate method involves authentication of the client at
       the SSL level using a certificate. For this to work, both the client
       and the server have certificates (which typically are different) and
       private keys.

       The API functions outlined above accept additional arguments that allow
       one to supply the client side certificate and key files. The format of
       these files is the same as used for server certificates and the caveat
       about encrypting private keys applies.

         ($page, $result, %headers) =                                   # 2c
                = get_https('www.bacus.pt', 443, '/protected.html',
                     make_headers(Authorization =>
                                  'Basic ' . MIME::Base64::encode("$user:$pass",'')),
                     '', $mime_type6, $path_to_crt7, $path_to_key8);

         ($page, $response, %reply_headers)
                = post_https('www.bacus.pt', 443, '/foo.cgi',           # 3b
                     make_headers('Authorization' =>
                                  'Basic ' . MIME::Base64::encode("$user:$pass",'')),
                     make_form(OK   => '1', name => 'Sampo'),
                     $mime_type6, $path_to_crt7, $path_to_key8);

       Case 2c (in SYNOPSIS) demonstrates getting a password protected page
       that also requires a client certificate, i.e. it is possible to use
       both authentication methods simultaneously.

       Case 3b (in SYNOPSIS) is a full blown POST to a secure server that
       requires both password authentication and a client certificate, just
       like in case 2c.

       Note: The client will not send a certificate unless the server requests
       one.  This is typically achieved by setting the verify mode to
       "VERIFY_PEER" on the server:

         Net::SSLeay::set_verify(ssl, Net::SSLeay::VERIFY_PEER, 0);

       See "perldoc ~openssl/doc/ssl/SSL_CTX_set_verify.pod" for a full
       description.

       Working through a web proxy

       o   set_proxy

       "Net::SSLeay" can use a web proxy to make its connections. You need to
       first set the proxy host and port using "set_proxy()" and then just use
       the normal API functions, e.g:

         Net::SSLeay::set_proxy('gateway.myorg.com', 8080);
         ($page) = get_https('www.bacus.pt', 443, '/');

       If your proxy requires authentication, you can supply a username and
       password as well

         Net::SSLeay::set_proxy('gateway.myorg.com', 8080, 'joe', 'salainen');
         ($page, $result, %headers) =
                = get_https('www.bacus.pt', 443, '/protected.html',
                     make_headers(Authorization =>
                                  'Basic ' . MIME::Base64::encode("susie:pass",''))
                     );

       This example demonstrates the case where we authenticate to the proxy
       as "joe" and to the final web server as "susie". Proxy authentication
       requires the "MIME::Base64" module to work.

       HTTP (without S) API

       o   get_http

       o   post_http

       o   tcpcat

       o   get_httpx

       o   post_httpx

       o   tcpxcat

       Over the years it has become clear that it would be convenient to use
       the light-weight flavour API of "Net::SSLeay" for normal HTTP as well
       (see "LWP" for the heavy-weight object-oriented approach). In fact it
       would be nice to be able to flip https on and off on the fly. Thus
       regular HTTP support was evolved.

         use Net::SSLeay qw(get_http post_http tcpcat
                             get_httpx post_httpx tcpxcat
                             make_headers make_form);

         ($page, $result, %headers)
                = get_http('www.bacus.pt', 443, '/protected.html',
                     make_headers(Authorization =>
                                  'Basic ' . MIME::Base64::encode("$user:$pass",''))
                     );

         ($page, $response, %reply_headers)
                = post_http('www.bacus.pt', 443, '/foo.cgi', '',
                       make_form(OK   => '1',
                                 name => 'Sampo'
                       ));

         ($reply, $err) = tcpcat($host, $port, $request);

         ($page, $result, %headers)
                = get_httpx($usessl, 'www.bacus.pt', 443, '/protected.html',
                     make_headers(Authorization =>
                                  'Basic ' . MIME::Base64::encode("$user:$pass",''))
                     );

         ($page, $response, %reply_headers)
                = post_httpx($usessl, 'www.bacus.pt', 443, '/foo.cgi', '',
                       make_form(OK   => '1',  name => 'Sampo' ));

         ($reply, $err, $server_cert) = tcpxcat($usessl, $host, $port, $request);

       As can be seen, the "x" family of APIs takes as the first argument a
       flag which indicates whether SSL is used or not.

   Certificate verification and Certificate Revocation Lists (CRLs)
       OpenSSL supports the ability to verify peer certificates. It can also
       optionally check the peer certificate against a Certificate Revocation
       List (CRL) from the certificates issuer. A CRL is a file, created by
       the certificate issuer that lists all the certificates that it
       previously signed, but which it now revokes. CRLs are in PEM format.

       You can enable "Net::SSLeay CRL" checking like this:

                   &Net::SSLeay::X509_STORE_set_flags
                       (&Net::SSLeay::CTX_get_cert_store($ssl),
                        &Net::SSLeay::X509_V_FLAG_CRL_CHECK);

       After setting this flag, if OpenSSL checks a peer's certificate, then
       it will attempt to find a CRL for the issuer. It does this by looking
       for a specially named file in the search directory specified by
       CTX_load_verify_locations.  CRL files are named with the hash of the
       issuer's subject name, followed by ".r0", ".r1" etc.  For example
       "ab1331b2.r0", "ab1331b2.r1". It will read all the .r files for the
       issuer, and then check for a revocation of the peer certificate in all
       of them.  (You can also force it to look in a specific named CRL file.,
       see below).  You can find out the hash of the issuer subject name in a
       CRL with

               openssl crl -in crl.pem -hash -noout

       If the peer certificate does not pass the revocation list, or if no CRL
       is found, then the handshaking fails with an error.

       You can also force OpenSSL to look for CRLs in one or more arbitrarily
       named files.

           my $bio = Net::SSLeay::BIO_new_file($crlfilename, 'r');
           my $crl = Net::SSLeay::PEM_read_bio_X509_CRL($bio);
           if ($crl) {
               Net::SSLeay::X509_STORE_add_crl(
                    Net::SSLeay::CTX_get_cert_store($ssl, $crl)
               );
           } else {
               error reading CRL....
           }

       Usually the URLs where you can download the CRLs is contained in the
       certificate itself and you can extract them with

           my @url = Net::SSLeay::P_X509_get_crl_distribution_points($cert)

       But there is no automatic downloading of the CRLs and often these CRLs
       are too huge to just download them to verify a single certificate.
       Also, these CRLs are often in DER format which you need to convert to
       PEM before you can use it:

           openssl crl -in crl.der -inform der -out crl.pem

       So as an alternative for faster and timely revocation checks you better
       use the Online Status Revocation Protocol (OCSP).

   Certificate verification and Online Status Revocation Protocol (OCSP)
       While checking for revoked certificates is possible and fast with
       Certificate Revocation Lists, you need to download the complete and
       often huge list before you can verify a single certificate.

       A faster way is to ask the CA to check the revocation of just a single
       or a few certificates using OCSP. Basically you generate for each
       certificate an OCSP_CERTID based on the certificate itself and its
       issuer, put the ids togetether into an OCSP_REQUEST and send the
       request to the URL given in the certificate.

       As a result you get back an OCSP_RESPONSE and need to check the status
       of the response, check that it is valid (e.g. signed by the CA) and
       finally extract the information about each OCSP_CERTID to find out if
       the certificate is still valid or got revoked.

       With Net::SSLeay this can be done like this:

           # get id(s) for given certs, like from get_peer_certificate
           # or get_peer_cert_chain. This will croak if
           # - one tries to make an OCSP_CERTID for a self-signed certificate
           # - the issuer of the certificate cannot be found in the SSL objects
           #   store, nor in the current certificate chain
           my $cert = Net::SSLeay::get_peer_certificate($ssl);
           my $id = eval { Net::SSLeay::OCSP_cert2ids($ssl,$cert) };
           die "failed to make OCSP_CERTID: $@" if $@;

           # create OCSP_REQUEST from id(s)
           # Multiple can be put into the same request, if the same OCSP responder
           # is responsible for them.
           my $req = Net::SSLeay::OCSP_ids2req($id);

           # determine URI of OCSP responder
           my $uri = Net::SSLeay::P_X509_get_ocsp_uri($cert);

           # Send stringified OCSP_REQUEST with POST to $uri.
           # We can ignore certificate verification for https, because the OCSP
           # response itself is signed.
           my $ua = HTTP::Tiny->new(verify_SSL => 0);
           my $res = $ua->request( 'POST',$uri, {
               headers => { 'Content-type' => 'application/ocsp-request' },
               content => Net::SSLeay::i2d_OCSP_REQUEST($req)
           });
           my $content = $res && $res->{success} && $res->{content}
               or die "query failed";

           # Extract OCSP_RESPONSE.
           # this will croak if the string is not an OCSP_RESPONSE
           my $resp = eval { Net::SSLeay::d2i_OCSP_RESPONSE($content) };

           # Check status of response.
           my $status = Net::SSLeay::OCSP_response_status($resp);
           if ($status != Net::SSLeay::OCSP_RESPONSE_STATUS_SUCCESSFUL())
               die "OCSP response failed: ".
                   Net::SSLeay::OCSP_response_status_str($status);
           }

           # Verify signature of response and if nonce matches request.
           # This will croak if there is a nonce in the response, but it does not match
           # the request. It will return false if the signature could not be verified,
           # in which case details can be retrieved with Net::SSLeay::ERR_get_error.
           # It will not complain if the response does not contain a nonce, which is
           # usually the case with pre-signed responses.
           if ( ! eval { Net::SSLeay::OCSP_response_verify($ssl,$resp,$req) }) {
               die "OCSP response verification failed";
           }

           # Extract information from OCSP_RESPONSE for each of the ids.

           # If called in scalar context it will return the time (as time_t), when the
           # next update is due (minimum of all successful responses inside $resp). It
           # will croak on the following problems:
           # - response is expired or not yet valid
           # - no response for given OCSP_CERTID
           # - certificate status is not good (e.g. revoked or unknown)
           if ( my $nextupd = eval { Net::SSLeay::OCSP_response_results($resp,$id) }) {
               warn "certificate is valid, next update in ".
                   ($nextupd-time())." seconds\n";
           } else {
               die "certificate is not valid: $@";
           }

           # But in array context it will return detailed information about each given
           # OCSP_CERTID instead croaking on errors:
           # if no @ids are given it will return information about all single responses
           # in the OCSP_RESPONSE
           my @results = Net::SSLeay::OCSP_response_results($resp,@ids);
           for my $r (@results) {
               print Dumper($r);
               # @results are in the same order as the @ids and contain:
               # $r->[0] - OCSP_CERTID
               # $r->[1] - undef if no error (certificate good) OR error message as string
               # $r->[2] - hash with details:
               #   thisUpdate - time_t of this single response
               #   nextUpdate - time_t when update is expected
               #   statusType - integer:
               #      V_OCSP_CERTSTATUS_GOOD(0)
               #      V_OCSP_CERTSTATUS_REVOKED(1)
               #      V_OCSP_CERTSTATUS_UNKNOWN(2)
               #   revocationTime - time_t (only if revoked)
               #   revocationReason - integer (only if revoked)
               #   revocationReason_str - reason as string (only if revoked)
           }

       To further speed up certificate revocation checking one can use a TLS
       extension to instruct the server to staple the OCSP response:

           # set TLS extension before doing SSL_connect
           Net::SSLeay::set_tlsext_status_type($ssl,
               Net::SSLeay::TLSEXT_STATUSTYPE_ocsp());

           # setup callback to verify OCSP response
           my $cert_valid = undef;
           Net::SSLeay::CTX_set_tlsext_status_cb($context,sub {
               my ($ssl,$resp) = @_;
               if (!$resp) {
                   # Lots of servers don't return an OCSP response.
                   # In this case we must check the OCSP status outside the SSL
                   # handshake.
                   warn "server did not return stapled OCSP response\n";
                   return 1;
               }
               # verify status
               my $status = Net::SSLeay::OCSP_response_status($resp);
               if ($status != Net::SSLeay::OCSP_RESPONSE_STATUS_SUCCESSFUL()) {
                   warn "OCSP response failure: $status\n";
                   return 1;
               }
               # verify signature - we have no OCSP_REQUEST here to check nonce
               if (!eval { Net::SSLeay::OCSP_response_verify($ssl,$resp) }) {
                   warn "OCSP response verify failed\n";
                   return 1;
               }
               # check if the certificate is valid
               # we should check here against the peer_certificate
               my $cert = Net::SSLeay::get_peer_certificate();
               my $certid = eval { Net::SSLeay::OCSP_cert2ids($ssl,$cert) } or do {
                   warn "cannot get certid from cert: $@";
                   $cert_valid = -1;
                   return 1;
               };

               if ( $nextupd = eval {
                   Net::SSLeay::OCSP_response_results($resp,$certid) }) {
                   warn "certificate not revoked\n";
                   $cert_valid = 1;
               } else {
                   warn "certificate not valid: $@";
                   $cert_valid = 0;
               }
           });

           # do SSL handshake here
           ....
           # check if certificate revocation was checked already
           if ( ! defined $cert_valid) {
               # check revocation outside of SSL handshake by asking OCSP responder
               ...
           } elsif ( ! $cert_valid ) {
               die "certificate not valid - closing SSL connection";
           } elsif ( $cert_valid<0 ) {
               die "cannot verify certificate revocation - self-signed ?";
           } else {
               # everything fine
               ...
           }

   Using Net::SSLeay in multi-threaded applications
       IMPORTANT: versions 1.42 or earlier are not thread-safe!

       Net::SSLeay module implements all necessary stuff to be ready for
       multi-threaded environment - it requires openssl-0.9.7 or newer. The
       implementation fully follows thread safety related requirements of
       openssl library(see <http://www.openssl.org/docs/crypto/threads.html>).

       If you are about to use Net::SSLeay (or any other module based on
       Net::SSLeay) in multi-threaded perl application it is recommended to
       follow this best-practice:

       Initialization

       Load and initialize Net::SSLeay module in the main thread:

           use threads;
           use Net::SSLeay;

           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

           sub do_master_job {
             #... call whatever from Net::SSLeay
           }

           sub do_worker_job {
             #... call whatever from Net::SSLeay
           }

           #start threads
           my $master  = threads->new(\&do_master_job, 'param1', 'param2');
           my @workers = threads->new(\&do_worker_job, 'arg1', 'arg2') for (1..10);

           #waiting for all threads to finish
           $_->join() for (threads->list);

       NOTE: Openssl's "int SSL_library_init(void)" function (which is also
       aliased as "SSLeay_add_ssl_algorithms", "OpenSSL_add_ssl_algorithms"
       and "add_ssl_algorithms") is not re-entrant and multiple calls can
       cause a crash in threaded application.  Net::SSLeay implements flags
       preventing repeated calls to this function, therefore even multiple
       initialization via Net::SSLeay::SSLeay_add_ssl_algorithms() should work
       without trouble.

       Using callbacks

       Do not use callbacks across threads (the module blocks cross-thread
       callback operations and throws a warning). Always do the callback
       setup, callback use and callback destruction within the same thread.

       Using openssl elements

       All openssl elements (X509, SSL_CTX, ...) can be directly passed
       between threads.

           use threads;
           use Net::SSLeay;

           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

           sub do_job {
             my $context = shift;
             Net::SSLeay::CTX_set_default_passwd_cb($context, sub { "secret" });
             #...
           }

           my $c = Net::SSLeay::CTX_new();
           threads->create(\&do_job, $c);

       Or:

           use threads;
           use Net::SSLeay;

           my $context; #does not need to be 'shared'

           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

           sub do_job {
             Net::SSLeay::CTX_set_default_passwd_cb($context, sub { "secret" });
             #...
           }

           $context = Net::SSLeay::CTX_new();
           threads->create(\&do_job);

       Using other perl modules based on Net::SSLeay

       It should be fine to use any other module based on Net::SSLeay (like
       IO::Socket::SSL) in multi-threaded applications. It is generally
       recommended to do any global initialization of such a module in the
       main thread before calling "threads->new(..)" or "threads->create(..)"
       but it might differ module by module.

       To be safe you can load and init Net::SSLeay explicitly in the main
       thread:

           use Net::SSLeay;
           use Other::SSLeay::Based::Module;

           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

       Or even safer:

           use Net::SSLeay;
           use Other::SSLeay::Based::Module;

           BEGIN {
             Net::SSLeay::load_error_strings();
             Net::SSLeay::SSLeay_add_ssl_algorithms();
             Net::SSLeay::randomize();
           }

       Combining Net::SSLeay with other modules linked with openssl

       BEWARE: This might be a big trouble! This is not guaranteed be thread-
       safe!

       There are many other (XS) modules linked directly to openssl library
       (like Crypt::SSLeay).

       As it is expected that also "another" module will call
       "SSLeay_add_ssl_algorithms" at some point we have again a trouble with
       multiple openssl initialization by Net::SSLeay and "another" module.

       As you can expect Net::SSLeay is not able to avoid multiple
       initialization of openssl library called by "another" module, thus you
       have to handle this on your own (in some cases it might not be possible
       at all to avoid this).

       Threading with get_https and friends

       The convenience functions get_https, post_https etc all initialize the
       SSL library by calling Net::SSLeay::initialize which does the
       conventional library initialization:

           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

       Net::SSLeay::initialize initializes the SSL library at most once.  You
       can override the Net::SSLeay::initialize function if you desire some
       other type of initialization behaviour by get_https and friends.  You
       can call Net::SSLeay::initialize from your own code if you desire this
       conventional library initialization.

   Convenience routines
       To be used with Low level API

           Net::SSLeay::randomize($rn_seed_file,$additional_seed);
           Net::SSLeay::set_cert_and_key($ctx, $cert_path, $key_path);
           $cert = Net::SSLeay::dump_peer_certificate($ssl);
           Net::SSLeay::ssl_write_all($ssl, $message) or die "ssl write failure";
           $got = Net::SSLeay::ssl_read_all($ssl) or die "ssl read failure";

           $got = Net::SSLeay::ssl_read_CRLF($ssl [, $max_length]);
           $got = Net::SSLeay::ssl_read_until($ssl [, $delimit [, $max_length]]);
           Net::SSLeay::ssl_write_CRLF($ssl, $message);

       o   randomize

           seeds the openssl PRNG with "/dev/urandom" (see the top of
           "SSLeay.pm" for how to change or configure this) and optionally
           with user provided data. It is very important to properly seed your
           random numbers, so do not forget to call this. The high level API
           functions automatically call "randomize()" so it is not needed with
           them. See also caveats.

       o   set_cert_and_key

           takes two file names as arguments and sets the certificate and
           private key to those. This can be used to set either server
           certificates or client certificates.

       o   dump_peer_certificate

           allows you to get a plaintext description of the certificate the
           peer (usually the server) presented to us.

       o   ssl_read_all

           see ssl_write_all (below)

       o   ssl_write_all

           "ssl_read_all()" and "ssl_write_all()" provide true blocking
           semantics for these operations (see limitation, below, for
           explanation). These are much preferred to the low level API
           equivalents (which implement BSD blocking semantics). The message
           argument to "ssl_write_all()" can be a reference. This is helpful
           to avoid unnecessary copying when writing something big, e.g:

               $data = 'A' x 1000000000;
               Net::SSLeay::ssl_write_all($ssl, \$data) or die "ssl write failed";

       o   ssl_read_CRLF

           uses "ssl_read_all()" to read in a line terminated with a carriage
           return followed by a linefeed (CRLF).  The CRLF is included in the
           returned scalar.

       o   ssl_read_until

           uses "ssl_read_all()" to read from the SSL input stream until it
           encounters a programmer specified delimiter.  If the delimiter is
           undefined, $/ is used.  If $/ is undefined, "\n" is used.  One can
           optionally set a maximum length of bytes to read from the SSL input
           stream.

       o   ssl_write_CRLF

           writes $message and appends CRLF to the SSL output stream.

   Initialization
       In order to use the low level API you should start your programs with
       the following incantation:

               use Net::SSLeay qw(die_now die_if_ssl_error);
               Net::SSLeay::load_error_strings();
               Net::SSLeay::SSLeay_add_ssl_algorithms();    # Important!
               Net::SSLeay::ENGINE_load_builtin_engines();  # If you want built-in engines
               Net::SSLeay::ENGINE_register_all_complete(); # If you want built-in engines
               Net::SSLeay::randomize();

   Error handling functions
       I can not emphasize the need to check for error enough. Use these
       functions even in the most simple programs, they will reduce debugging
       time greatly. Do not ask questions on the mailing list without having
       first sprinkled these in your code.

       o   die_now

       o   die_if_ssl_error

           "die_now()" and "die_if_ssl_error()" are used to conveniently print
           the SSLeay error stack when something goes wrong:

                   Net::SSLeay::connect($ssl) or die_now("Failed SSL connect ($!)");


                   Net::SSLeay::write($ssl, "foo") or die_if_ssl_error("SSL write ($!)");

       o   print_errs

           You can also use "Net::SSLeay::print_errs()" to dump the error
           stack without exiting the program. As can be seen, your code
           becomes much more readable if you import the error reporting
           functions into your main name space.

   Sockets
       Perl uses file handles for all I/O. While SSLeay has a quite flexible
       BIO mechanism and perl has an evolved PerlIO mechanism, this module
       still sticks to using file descriptors. Thus to attach SSLeay to a
       socket you should use "fileno()" to extract the underlying file
       descriptor:

           Net::SSLeay::set_fd($ssl, fileno(S));   # Must use fileno

       You should also set $| to 1 to eliminate STDIO buffering so you do not
       get confused if you use perl I/O functions to manipulate your socket
       handle.

       If you need to select(2) on the socket, go right ahead, but be warned
       that OpenSSL does some internal buffering so SSL_read does not always
       return data even if the socket selected for reading (just keep on
       selecting and trying to read). "Net::SSLeay" is no different from the C
       language OpenSSL in this respect.

   Callbacks
       You can establish a per-context verify callback function something like
       this:

               sub verify {
                   my ($ok, $x509_store_ctx) = @_;
                   print "Verifying certificate...\n";
                       ...
                   return $ok;
               }

       It is used like this:

               Net::SSLeay::set_verify ($ssl, Net::SSLeay::VERIFY_PEER, \&verify);

       Per-context callbacks for decrypting private keys are implemented.

               Net::SSLeay::CTX_set_default_passwd_cb($ctx, sub { "top-secret" });
               Net::SSLeay::CTX_use_PrivateKey_file($ctx, "key.pem",
                                                    Net::SSLeay::FILETYPE_PEM)
                   or die "Error reading private key";
               Net::SSLeay::CTX_set_default_passwd_cb($ctx, undef);

       If Hello Extensions are supported by your OpenSSL, a session secret
       callback can be set up to be called when a session secret is set by
       openssl.

       Establish it like this:
           Net::SSLeay::set_session_secret_cb($ssl, \&session_secret_cb,
       $somedata);

       It will be called like this:

           sub session_secret_cb
           {
               my ($secret, \@cipherlist, \$preferredcipher, $somedata) = @_;
           }

       No other callbacks are implemented. You do not need to use any callback
       for simple (i.e. normal) cases where the SSLeay built-in verify
       mechanism satisfies your needs.

       It is required to reset these callbacks to undef immediately after use
       to prevent memory leaks, thread safety problems and crashes on exit
       that can occur if different threads set different callbacks.

       If you want to use callback stuff, see examples/callback.pl! It's the
       only one I am able to make work reliably.

   Low level API
       In addition to the high level functions outlined above, this module
       contains straight-forward access to CRYPTO and SSL parts of OpenSSL C
       API.

       See the "*.h" headers from OpenSSL C distribution for a list of low
       level SSLeay functions to call (check SSLeay.xs to see if some function
       has been implemented). The module strips the initial "SSL_" off of the
       SSLeay names.  Generally you should use "Net::SSLeay::" in its place.

       Note that some functions are prefixed with "P_" - these are very close
       to the original API however contain some kind of a wrapper making its
       interface more perl friendly.

       For example:

       In C:

               #include <ssl.h>

               err = SSL_set_verify (ssl, SSL_VERIFY_CLIENT_ONCE,
                                          &your_call_back_here);

       In Perl:

               use Net::SSLeay;

               $err = Net::SSLeay::set_verify ($ssl,
                                               Net::SSLeay::VERIFY_CLIENT_ONCE,
                                               \&your_call_back_here);

       If the function does not start with "SSL_" you should use the full
       function name, e.g.:

               $err = Net::SSLeay::ERR_get_error;

       The following new functions behave in perlish way:

               $got = Net::SSLeay::read($ssl);
                                           # Performs SSL_read, but returns $got
                                           # resized according to data received.
                                           # Returns undef on failure.

               Net::SSLeay::write($ssl, $foo) || die;
                                           # Performs SSL_write, but automatically
                                           # figures out the size of $foo

       Low level API: Version related functions

       o   SSLeay

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           Gives version number (numeric) of underlaying openssl library.

            my $ver_number = Net::SSLeay::SSLeay();
            # returns: the number identifying the openssl release
            #
            # 0x00903100 => openssl-0.9.3
            # 0x00904100 => openssl-0.9.4
            # 0x00905100 => openssl-0.9.5
            # 0x0090600f => openssl-0.9.6
            # 0x0090601f => openssl-0.9.6a
            # 0x0090602f => openssl-0.9.6b
            # ...
            # 0x009060df => openssl-0.9.6m
            # 0x0090700f => openssl-0.9.7
            # 0x0090701f => openssl-0.9.7a
            # 0x0090702f => openssl-0.9.7b
            # ...
            # 0x009070df => openssl-0.9.7m
            # 0x0090800f => openssl-0.9.8
            # 0x0090801f => openssl-0.9.8a
            # 0x0090802f => openssl-0.9.8b
            # ...
            # 0x0090814f => openssl-0.9.8t
            # 0x1000000f => openssl-1.0.0
            # 0x1000004f => openssl-1.0.0d
            # 0x1000007f => openssl-1.0.0g

           You can use it like this:

             if (Net::SSLeay::SSLeay() < 0x0090800f) {
               die "you need openssl-0.9.8 or higher";
             }

       o   SSLeay_version

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           Gives version number (string) of underlaying openssl library.

            my $ver_string = Net::SSLeay::SSLeay_version($type);
            # $type
            #   0 (=SSLEAY_VERSION) - e.g. 'OpenSSL 1.0.0d 8 Feb 2011'
            #   2 (=SSLEAY_CFLAGS)  - e.g. 'compiler: gcc -D_WINDLL -DOPENSSL_USE_APPLINK .....'
            #   3 (=SSLEAY_BUILT_ON)- e.g. 'built on: Fri May  6 00:00:46 GMT 2011'
            #   4 (=SSLEAY_PLATFORM)- e.g. 'platform: mingw'
            #
            # returns: string

            Net::SSLeay::SSLeay_version();
            #is equivalent to
            Net::SSLeay::SSLeay_version(0);

           Check openssl doc
           <http://www.openssl.org/docs/crypto/SSLeay_version.html>

       Low level API: Initialization related functions

       o   library_init

           Initialize SSL library by registering algorithms.

            my $rv = Net::SSLeay::library_init();

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_library_init.html>

           While the original function from OpenSSL always returns 1,
           Net::SSLeay adds a wrapper around it to make sure that the OpenSSL
           function is only called once.  Thus the function will return 1 if
           initialization was done and 0 if not, i.e. if initialization was
           done already before.

       o   add_ssl_algorithms

           The alias for "library_init"

            Net::SSLeay::add_ssl_algorithms();

       o   OpenSSL_add_ssl_algorithms

           The alias for "library_init"

            Net::SSLeay::OpenSSL_add_ssl_algorithms();

       o   SSLeay_add_ssl_algorithms

           The alias for "library_init"

            Net::SSLeay::SSLeay_add_ssl_algorithms();

       o   load_error_strings

           Registers the error strings for all libcrypto + libssl related
           functions.

            Net::SSLeay::load_error_strings();
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/ERR_load_crypto_strings.html>

       o   ERR_load_crypto_strings

           Registers the error strings for all libcrypto functions. No need to
           call this function if you have already called "load_error_strings".

            Net::SSLeay::ERR_load_crypto_strings();
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/ERR_load_crypto_strings.html>

       o   ERR_load_RAND_strings

           Registers the error strings for RAND related functions. No need to
           call this function if you have already called "load_error_strings".

            Net::SSLeay::ERR_load_RAND_strings();
            #
            # returns: no return value

       o   ERR_load_SSL_strings

           Registers the error strings for SSL related functions. No need to
           call this function if you have already called "load_error_strings".

            Net::SSLeay::ERR_load_SSL_strings();
            #
            # returns: no return value

       o   OpenSSL_add_all_algorithms

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Add algorithms to internal table.

            Net::SSLeay::OpenSSL_add_all_algorithms();
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/OpenSSL_add_all_algorithms.html>

       o   OPENSSL_add_all_algorithms_conf

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Similar to "OpenSSL_add_all_algorithms" - will ALWAYS load the
           config file

            Net::SSLeay::OPENSSL_add_all_algorithms_conf();
            #
            # returns: no return value

       o   OPENSSL_add_all_algorithms_noconf

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Similar to "OpenSSL_add_all_algorithms" - will NEVER load the
           config file

            Net::SSLeay::OPENSSL_add_all_algorithms_noconf();
            #
            # returns: no return value

       Low level API: ERR_* and SSL_alert_* related functions

       NOTE: Please note that SSL_alert_* function have "SSL_" part stripped
       from their names.

       o   ERR_clear_error

           Clear the error queue.

            Net::SSLeay::ERR_clear_error();
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/ERR_clear_error.html>

       o   ERR_error_string

           Generates a human-readable string representing the error code
           $error.

            my $rv = Net::SSLeay::ERR_error_string($error);
            # $error - (unsigned integer) error code
            #
            # returns: string

           Check openssl doc
           <http://www.openssl.org/docs/crypto/ERR_error_string.html>

       o   ERR_get_error

           Returns the earliest error code from the thread's error queue and
           removes the entry.  This function can be called repeatedly until
           there are no more error codes to return.

            my $rv = Net::SSLeay::ERR_get_error();
            #
            # returns: (unsigned integer) error code

           Check openssl doc
           <http://www.openssl.org/docs/crypto/ERR_get_error.html>

       o   ERR_peek_error

           Returns the earliest error code from the thread's error queue
           without modifying it.

            my $rv = Net::SSLeay::ERR_peek_error();
            #
            # returns: (unsigned integer) error code

           Check openssl doc
           <http://www.openssl.org/docs/crypto/ERR_get_error.html>

       o   ERR_put_error

           Adds an error code to the thread's error queue. It signals that the
           error of $reason code reason occurred in function $func of library
           $lib, in line number $line of $file.

            Net::SSLeay::ERR_put_error($lib, $func, $reason, $file, $line);
            # $lib - (integer) library id (check openssl/err.h for constants e.g. ERR_LIB_SSL)
            # $func - (integer) function id (check openssl/ssl.h for constants e.g. SSL_F_SSL23_READ)
            # $reason - (integer) reason id (check openssl/ssl.h for constants e.g. SSL_R_SSL_HANDSHAKE_FAILURE)
            # $file - (string) file name
            # $line - (integer) line number in $file
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/ERR_put_error.html> and
           <http://www.openssl.org/docs/crypto/err.html>

       o   alert_desc_string

           Returns a two letter string as a short form describing the reason
           of the alert specified by value.

            my $rv = Net::SSLeay::alert_desc_string($value);
            # $value - (integer) allert id (check openssl/ssl.h for SSL3_AD_* and TLS1_AD_* constants)
            #
            # returns: description string (2 letters)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_alert_type_string.html>

       o   alert_desc_string_long

           Returns a string describing the reason of the alert specified by
           value.

            my $rv = Net::SSLeay::alert_desc_string_long($value);
            # $value - (integer) allert id (check openssl/ssl.h for SSL3_AD_* and TLS1_AD_* constants)
            #
            # returns: description string

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_alert_type_string.html>

       o   alert_type_string

           Returns a one letter string indicating the type of the alert
           specified by value.

            my $rv = Net::SSLeay::alert_type_string($value);
            # $value - (integer) allert id (check openssl/ssl.h for SSL3_AD_* and TLS1_AD_* constants)
            #
            # returns: string (1 letter)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_alert_type_string.html>

       o   alert_type_string_long

           Returns a string indicating the type of the alert specified by
           value.

            my $rv = Net::SSLeay::alert_type_string_long($value);
            # $value - (integer) allert id (check openssl/ssl.h for SSL3_AD_* and TLS1_AD_* constants)
            #
            # returns: string

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_alert_type_string.html>

       Low level API: SSL_METHOD_* related functions

       o   SSLv2_method

           Returns SSL_METHOD structure corresponding to SSLv2 method, the
           return value can be later used as a param of "CTX_new_with_method".
           Only available where supported by the underlying openssl.

            my $rv = Net::SSLeay::SSLv2_method();
            #
            # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

       o   SSLv3_method

           Returns SSL_METHOD structure corresponding to SSLv3 method, the
           return value can be later used as a param of "CTX_new_with_method".

            my $rv = Net::SSLeay::SSLv3_method();
            #
            # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_new.html>

       o   TLSv1_method

           Returns SSL_METHOD structure corresponding to TLSv1 method, the
           return value can be later used as a param of "CTX_new_with_method".

            my $rv = Net::SSLeay::TLSv1_method();
            #
            # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_new.html>

       o   TLSv1_1_method

           Returns SSL_METHOD structure corresponding to TLSv1_1 method, the
           return value can be later used as a param of "CTX_new_with_method".
           Only available where supported by the underlying openssl.

            my $rv = Net::SSLeay::TLSv1__1method();
            #
            # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_new.html>

       o   TLSv1_2_method

           Returns SSL_METHOD structure corresponding to TLSv1_2 method, the
           return value can be later used as a param of "CTX_new_with_method".
           Only available where supported by the underlying openssl.

            my $rv = Net::SSLeay::TLSv1_2_method();
            #
            # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_new.html>

       Low level API: ENGINE_* related functions

       o   ENGINE_load_builtin_engines

           Load all bundled ENGINEs into memory and make them visible.

            Net::SSLeay::ENGINE_load_builtin_engines();
            #
            # returns: no return value

           Check openssl doc <http://www.openssl.org/docs/crypto/engine.html>

       o   ENGINE_register_all_complete

           Register all loaded ENGINEs for every algorithm they collectively
           implement.

            Net::SSLeay::ENGINE_register_all_complete();
            #
            # returns: no return value

           Check openssl doc <http://www.openssl.org/docs/crypto/engine.html>

       o   ENGINE_set_default

           Set default engine to $e + set its flags to $flags.

            my $rv = Net::SSLeay::ENGINE_set_default($e, $flags);
            # $e - value corresponding to openssl's ENGINE structure
            # $flags - (integer) engine flags
            #          flags value can be made by bitwise "OR"ing:
            #          0x0001 - ENGINE_METHOD_RSA
            #          0x0002 - ENGINE_METHOD_DSA
            #          0x0004 - ENGINE_METHOD_DH
            #          0x0008 - ENGINE_METHOD_RAND
            #          0x0010 - ENGINE_METHOD_ECDH
            #          0x0020 - ENGINE_METHOD_ECDSA
            #          0x0040 - ENGINE_METHOD_CIPHERS
            #          0x0080 - ENGINE_METHOD_DIGESTS
            #          0x0100 - ENGINE_METHOD_STORE
            #          0x0200 - ENGINE_METHOD_PKEY_METHS
            #          0x0400 - ENGINE_METHOD_PKEY_ASN1_METHS
            #          Obvious all-or-nothing cases:
            #          0xFFFF - ENGINE_METHOD_ALL
            #          0x0000 - ENGINE_METHOD_NONE
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc <http://www.openssl.org/docs/crypto/engine.html>

       o   ENGINE_by_id

           Get ENGINE by its identification $id.

            my $rv = Net::SSLeay::ENGINE_by_id($id);
            # $id - (string) engine identification e.g. "dynamic"
            #
            # returns: value corresponding to openssl's ENGINE structure (0 on failure)

           Check openssl doc <http://www.openssl.org/docs/crypto/engine.html>

       Low level API: EVP_PKEY_* related functions

       o   EVP_PKEY_copy_parameters

           Copies the parameters from key $from to key $to.

            my $rv = Net::SSLeay::EVP_PKEY_copy_parameters($to, $from);
            # $to - value corresponding to openssl's EVP_PKEY structure
            # $from - value corresponding to openssl's EVP_PKEY structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/crypto/EVP_PKEY_cmp.html>

       o   EVP_PKEY_new

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Creates a new EVP_PKEY structure.

            my $rv = Net::SSLeay::EVP_PKEY_new();
            #
            # returns: value corresponding to openssl's EVP_PKEY structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/EVP_PKEY_new.html>

       o   EVP_PKEY_free

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Free an allocated EVP_PKEY structure.

            Net::SSLeay::EVP_PKEY_free($pkey);
            # $pkey - value corresponding to openssl's EVP_PKEY structure
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/EVP_PKEY_new.html>

       o   EVP_PKEY_assign_RSA

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Set the key referenced by $pkey to $key

           NOTE: No reference counter will be increased, i.e. $key will be
           freed if $pkey is freed.

            my $rv = Net::SSLeay::EVP_PKEY_assign_RSA($pkey, $key);
            # $pkey - value corresponding to openssl's EVP_PKEY structure
            # $key - value corresponding to openssl's RSA structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/crypto/EVP_PKEY_assign_RSA.html>

       o   EVP_PKEY_assign_EC_KEY

           COMPATIBILITY: not available in Net-SSLeay-1.74 and before

           Set the key referenced by $pkey to $key

           NOTE: No reference counter will be increased, i.e. $key will be
           freed if $pkey is freed.

            my $rv = Net::SSLeay::EVP_PKEY_assign_EC_KEY($pkey, $key);
            # $pkey - value corresponding to openssl's EVP_PKEY structure
            # $key - value corresponding to openssl's EC_KEY structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/crypto/EVP_PKEY_assign_EC_KEY.html>

       o   EVP_PKEY_bits

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns the size of the key $pkey in bits.

            my $rv = Net::SSLeay::EVP_PKEY_bits($pkey);
            # $pkey - value corresponding to openssl's EVP_PKEY structure
            #
            # returns: size in bits

       o   EVP_PKEY_size

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns the maximum size of a signature in bytes. The actual
           signature may be smaller.

            my $rv = Net::SSLeay::EVP_PKEY_size($pkey);
            # $pkey - value corresponding to openssl's EVP_PKEY structure
            #
            # returns: the maximum size in bytes

           Check openssl doc
           <http://www.openssl.org/docs/crypto/EVP_SignInit.html>

       o   EVP_PKEY_id

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-1.0.0

           Returns $pkey type (integer value of corresponding NID).

            my $rv = Net::SSLeay::EVP_PKEY_id($pkey);
            # $pkey - value corresponding to openssl's EVP_PKEY structure
            #
            # returns: (integer) key type

           Example:

            my $pubkey = Net::SSLeay::X509_get_pubkey($x509);
            my $type = Net::SSLeay::EVP_PKEY_id($pubkey);
            print Net::SSLeay::OBJ_nid2sn($type);             #prints e.g. 'rsaEncryption'

       Low level API: PEM_* related functions

       Check openssl doc <http://www.openssl.org/docs/crypto/pem.html>

       o   PEM_read_bio_X509

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Loads PEM formatted X509 certificate via given BIO structure.

            my $rv = Net::SSLeay::PEM_read_bio_X509($bio);
            # $bio - value corresponding to openssl's BIO structure
            #
            # returns: value corresponding to openssl's X509 structure (0 on failure)

           Example:

            my $bio = Net::SSLeay::BIO_new_file($filename, 'r');
            my $x509 = Net::SSLeay::PEM_read_bio_X509($bio);
            Net::SSLeay::BIO_free($bio);

       o   PEM_read_bio_X509_REQ

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Loads PEM formatted X509_REQ object via given BIO structure.

            my $rv = Net::SSLeay::PEM_read_bio_X509_REQ($bio, $x=NULL, $cb=NULL, $u=NULL);
            # $bio - value corresponding to openssl's BIO structure
            #
            # returns: value corresponding to openssl's X509_REQ structure (0 on failure)

           Example:

            my $bio = Net::SSLeay::BIO_new_file($filename, 'r');
            my $x509_req = Net::SSLeay::PEM_read_bio_X509_REQ($bio);
            Net::SSLeay::BIO_free($bio);

       o   PEM_read_bio_DHparams

           Reads DH structure from BIO.

            my $rv = Net::SSLeay::PEM_read_bio_DHparams($bio);
            # $bio - value corresponding to openssl's BIO structure
            #
            # returns: value corresponding to openssl's DH structure (0 on failure)

       o   PEM_read_bio_X509_CRL

           Reads X509_CRL structure from BIO.

            my $rv = Net::SSLeay::PEM_read_bio_X509_CRL($bio);
            # $bio - value corresponding to openssl's BIO structure
            #
            # returns: value corresponding to openssl's X509_CRL structure (0 on failure)

       o   PEM_read_bio_PrivateKey

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Loads PEM formatted private key via given BIO structure.

            my $rv = Net::SSLeay::PEM_read_bio_PrivateKey($bio, $cb, $data);
            # $bio - value corresponding to openssl's BIO structure
            # $cb - reference to perl callback function
            # $data - data that will be passed to callback function (see examples below)
            #
            # returns: value corresponding to openssl's EVP_PKEY structure (0 on failure)

           Example:

            my $bio = Net::SSLeay::BIO_new_file($filename, 'r');
            my $privkey = Net::SSLeay::PEM_read_bio_PrivateKey($bio); #ask for password if needed
            Net::SSLeay::BIO_free($bio);

           To use password you have the following options:

            $privkey = Net::SSLeay::PEM_read_bio_PrivateKey($bio, \&callback_func); # use callback func for getting password
            $privkey = Net::SSLeay::PEM_read_bio_PrivateKey($bio, \&callback_func, $data); # use callback_func + pass $data to callback_func
            $privkey = Net::SSLeay::PEM_read_bio_PrivateKey($bio, undef, "secret"); # use password "secret"
            $privkey = Net::SSLeay::PEM_read_bio_PrivateKey($bio, undef, "");       # use empty password

           Callback function signature:

            sub callback_func {
              my ($max_passwd_size, $rwflag, $data) = @_;
              # $max_passwd_size - maximum size of returned password (longer values will be discarded)
              # $rwflag - indicates whether we are loading (0) or storing (1) - for PEM_read_bio_PrivateKey always 0
              # $data - the data passed to PEM_read_bio_PrivateKey as 3rd parameter

              return "secret";
            }

       o   PEM_get_string_X509

           NOTE: Does not exactly correspond to any low level API function

           Converts/exports X509 certificate to string (PEM format).

            Net::SSLeay::PEM_get_string_X509($x509);
            # $x509 - value corresponding to openssl's X509 structure
            #
            # returns: string with $x509 in PEM format

       o   PEM_get_string_PrivateKey

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Converts public key $pk into PEM formatted string (optionally
           protected with password).

            my $rv = Net::SSLeay::PEM_get_string_PrivateKey($pk, $passwd, $enc_alg);
            # $pk - value corresponding to openssl's EVP_PKEY structure
            # $passwd - [optional] (string) password to use for key encryption
            # $enc_alg - [optional] algorithm to use for key encryption (default: DES_CBC) - value corresponding to openssl's EVP_CIPHER structure
            #
            # returns: PEM formatted string

           Examples:

            $pem_privkey = Net::SSLeay::PEM_get_string_PrivateKey($pk);
            $pem_privkey = Net::SSLeay::PEM_get_string_PrivateKey($pk, "secret");
            $pem_privkey = Net::SSLeay::PEM_get_string_PrivateKey($pk, "secret", Net::SSLeay::EVP_get_cipherbyname("DES-EDE3-CBC"));

       o   PEM_get_string_X509_CRL

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Converts X509_CRL object $x509_crl into PEM formatted string.

            Net::SSLeay::PEM_get_string_X509_CRL($x509_crl);
            # $x509_crl - value corresponding to openssl's X509_CRL structure
            #
            # returns: no return value

       o   PEM_get_string_X509_REQ

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Converts X509_REQ object $x509_crl into PEM formatted string.

            Net::SSLeay::PEM_get_string_X509_REQ($x509_req);
            # $x509_req - value corresponding to openssl's X509_REQ structure
            #
            # returns: no return value

       Low level API: d2i_* (DER format) related functions

       o   d2i_X509_bio

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Loads DER formatted X509 certificate via given BIO structure.

            my $rv = Net::SSLeay::d2i_X509_bio($bp);
            # $bp - value corresponding to openssl's BIO structure
            #
            # returns: value corresponding to openssl's X509 structure (0 on failure)

           Example:

            my $bio = Net::SSLeay::BIO_new_file($filename, 'rb');
            my $x509 = Net::SSLeay::d2i_X509_bio($bio);
            Net::SSLeay::BIO_free($bio);

           Check openssl doc
           <http://www.openssl.org/docs/crypto/d2i_X509.html>

       o   d2i_X509_CRL_bio

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Loads DER formatted X509_CRL object via given BIO structure.

            my $rv = Net::SSLeay::d2i_X509_CRL_bio($bp);
            # $bp - value corresponding to openssl's BIO structure
            #
            # returns: value corresponding to openssl's X509_CRL structure (0 on failure)

           Example:

            my $bio = Net::SSLeay::BIO_new_file($filename, 'rb');
            my $x509_crl = Net::SSLeay::d2i_X509_CRL_bio($bio);
            Net::SSLeay::BIO_free($bio);

       o   d2i_X509_REQ_bio

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Loads DER formatted X509_REQ object via given BIO structure.

            my $rv = Net::SSLeay::d2i_X509_REQ_bio($bp);
            # $bp - value corresponding to openssl's BIO structure
            #
            # returns: value corresponding to openssl's X509_REQ structure (0 on failure)

           Example:

            my $bio = Net::SSLeay::BIO_new_file($filename, 'rb');
            my $x509_req = Net::SSLeay::d2i_X509_REQ_bio($bio);
            Net::SSLeay::BIO_free($bio);

       Low level API: PKCS12 related functions

       o   P_PKCS12_load_file

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Loads X509 certificate + private key + certificates of CA chain (if
           present in PKCS12 file).

            my ($privkey, $cert, @cachain) = Net::SSLeay::P_PKCS12_load_file($filename, $load_chain, $password);
            # $filename - name of PKCS12 file
            # $load_chain - [optional] whether load (1) or not(0) CA chain (default: 0)
            # $password - [optional] password for private key
            #
            # returns: triplet ($privkey, $cert, @cachain)
            #          $privkey - value corresponding to openssl's EVP_PKEY structure
            #          $cert - value corresponding to openssl's X509 structure
            #          @cachain - array of values corresponding to openssl's X509 structure (empty if no CA chain in PKCS12)

           IMPORTANT NOTE: after you do the job you need to call X509_free()
           on $privkey + all members of @cachain and EVP_PKEY_free() on
           $privkey.

           Examples:

            my ($privkey, $cert) = Net::SSLeay::P_PKCS12_load_file($filename);
            #or
            my ($privkey, $cert) = Net::SSLeay::P_PKCS12_load_file($filename, 0, $password);
            #or
            my ($privkey, $cert, @cachain) = Net::SSLeay::P_PKCS12_load_file($filename, 1);
            #or
            my ($privkey, $cert, @cachain) = Net::SSLeay::P_PKCS12_load_file($filename, 1, $password);

            #BEWARE: THIS IS WRONG - MEMORY LEAKS! (you cannot free @cachain items)
            my ($privkey, $cert) = Net::SSLeay::P_PKCS12_load_file($filename, 1, $password);

           NOTE With some combinations of Windows, perl, compiler and compiler
           options, you may see a runtime error "no OPENSSL_Applink", when
           calling Net::SSLeay::P_PKCS12_load_file. See README.Win32 for more
           details.

       Low level API: SESSION_* related functions

       o   d2i_SSL_SESSION

           Transforms the external ASN1 representation of an SSL/TLS session,
           stored as binary data at location pp with length of $length, into
           an SSL_SESSION object.

           ??? (does this function really work?)

            my $rv = Net::SSLeay::d2i_SSL_SESSION($a, $pp, $length);
            # $a - value corresponding to openssl's SSL_SESSION structure
            # $pp - pointer/buffer ???
            # $length - ???
            #
            # returns: ???

           Check openssl doc
           <http://www.openssl.org/docs/ssl/d2i_SSL_SESSION.html>

       o   i2d_SSL_SESSION

           Transforms the SSL_SESSION object in into the ASN1 representation
           and stores it into the memory location pointed to by pp. The length
           of the resulting ASN1 representation is returned.

           ??? (does this function really work?)

            my $rv = Net::SSLeay::i2d_SSL_SESSION($in, $pp);
            # $in - value corresponding to openssl's SSL_SESSION structure
            # $pp - pointer/data ???
            #
            # returns: 1 on success, 0

           Check openssl doc
           <http://www.openssl.org/docs/ssl/d2i_SSL_SESSION.html>

       o   SESSION_new

           Creates a new SSL_SESSION structure.

            my $rv = Net::SSLeay::SESSION_new();
            #
            # returns: value corresponding to openssl's SSL_SESSION structure (0 on failure)

       o   SESSION_free

           Free an allocated SSL_SESSION structure.

            Net::SSLeay::SESSION_free($ses);
            # $ses - value corresponding to openssl's SSL_SESSION structure
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_SESSION_free.html>

       o   SESSION_cmp

           Compare two SSL_SESSION structures.

            my $rv = Net::SSLeay::SESSION_cmp($sesa, $sesb);
            # $sesa - value corresponding to openssl's SSL_SESSION structure
            # $sesb - value corresponding to openssl's SSL_SESSION structure
            #
            # returns: 0 if the two structures are the same

           NOTE: Not available in openssl 1.0 or later

       o   SESSION_get_app_data

           Can be used to get application defined value/data.

            my $rv = Net::SSLeay::SESSION_get_app_data($ses);
            # $ses - value corresponding to openssl's SSL_SESSION structure
            #
            # returns: string/buffer/pointer ???

       o   SESSION_set_app_data

           Can be used to set some application defined value/data.

            my $rv = Net::SSLeay::SESSION_set_app_data($s, $a);
            # $s - value corresponding to openssl's SSL_SESSION structure
            # $a - (string/buffer/pointer ???) data
            #
            # returns: ???

       o   SESSION_get_ex_data

           Is used to retrieve the information for $idx from session $ses.

            my $rv = Net::SSLeay::SESSION_get_ex_data($ses, $idx);
            # $ses - value corresponding to openssl's SSL_SESSION structure
            # $idx - (integer) index for application specific data
            #
            # returns: pointer to ???

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_SESSION_get_ex_new_index.html>

       o   SESSION_set_ex_data

           Is used to store application data at arg for idx into the session
           object.

            my $rv = Net::SSLeay::SESSION_set_ex_data($ss, $idx, $data);
            # $ss - value corresponding to openssl's SSL_SESSION structure
            # $idx - (integer) ???
            # $data - (pointer) ???
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_SESSION_get_ex_new_index.html>

       o   SESSION_get_ex_new_index

           Is used to register a new index for application specific data.

            my $rv = Net::SSLeay::SESSION_get_ex_new_index($argl, $argp, $new_func, $dup_func, $free_func);
            # $argl - (long) ???
            # $argp - (pointer) ???
            # $new_func - function pointer ??? (CRYPTO_EX_new *)
            # $dup_func - function pointer ??? (CRYPTO_EX_dup *)
            # $free_func - function pointer ??? (CRYPTO_EX_free *)
            #
            # returns: (integer) ???

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_SESSION_get_ex_new_index.html>

       o   SESSION_get_master_key

           NOTE: Does not exactly correspond to any low level API function

           Returns 'master_key' value from SSL_SESSION structure $s

            Net::SSLeay::SESSION_get_master_key($s);
            # $s - value corresponding to openssl's SSL_SESSION structure
            #
            # returns: master key (binary data)

       o   SESSION_set_master_key

           Sets 'master_key' value for SSL_SESSION structure $s

            Net::SSLeay::SESSION_set_master_key($s, $key);
            # $s - value corresponding to openssl's SSL_SESSION structure
            # $key - master key (binary data)
            #
            # returns: no return value

           Not available with OpenSSL 1.1 and later.  Code that previously
           used
                  SESSION_set_master_key must now set $secret in the
           session_secret
                  callback set with SSL_set_session_secret_cb.

       o   SESSION_get_time

           Returns the time at which the session s was established.  The time
           is given in seconds since 1.1.1970.

            my $rv = Net::SSLeay::SESSION_get_time($s);
            # $s - value corresponding to openssl's SSL_SESSION structure
            #
            # returns: timestamp (seconds since 1.1.1970)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_SESSION_get_time.html>

       o   get_time

           Technically the same functionality as "SESSION_get_time".

            my $rv = Net::SSLeay::get_time($s);

       o   SESSION_get_timeout

           Returns the timeout value set for session $s in seconds.

            my $rv = Net::SSLeay::SESSION_get_timeout($s);
            # $s - value corresponding to openssl's SSL_SESSION structure
            #
            # returns: timeout (in seconds)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_SESSION_get_time.html>

       o   get_timeout

           Technically the same functionality as "SESSION_get_timeout".

            my $rv = Net::SSLeay::get_timeout($s);

       o   SESSION_print

           NOTE: Does not exactly correspond to any low level API function

           Prints session details (e.g. protocol version, cipher, session-id
           ...) to BIO.

            my $rv = Net::SSLeay::SESSION_print($fp, $ses);
            # $fp - value corresponding to openssl's BIO structure
            # $ses - value corresponding to openssl's SSL_SESSION structure
            #
            # returns: 1 on success, 0 on failure

           You have to use necessary BIO functions like this:

            # let us have $ssl corresponding to openssl's SSL structure
            my $ses = Net::SSLeay::get_session($ssl);
            my $bio = Net::SSLeay::BIO_new(&Net::SSLeay::BIO_s_mem);
            Net::SSLeay::SESSION_print($bio, $ses);
            print Net::SSLeay::BIO_read($bio);

       o   SESSION_print_fp

           Prints session details (e.g. protocol version, cipher, session-id
           ...) to file handle.

            my $rv = Net::SSLeay::SESSION_print_fp($fp, $ses);
            # $fp - perl file handle
            # $ses - value corresponding to openssl's SSL_SESSION structure
            #
            # returns: 1 on success, 0 on failure

           Example:

            # let us have $ssl corresponding to openssl's SSL structure
            my $ses = Net::SSLeay::get_session($ssl);
            open my $fh, ">", "output.txt";
            Net::SSLeay::SESSION_print_fp($fh,$ses);

       o   SESSION_set_time

           Replaces the creation time of the session s with the chosen value
           $t (seconds since 1.1.1970).

            my $rv = Net::SSLeay::SESSION_set_time($ses, $t);
            # $ses - value corresponding to openssl's SSL_SESSION structure
            # $t - time value
            #
            # returns: 1 on success

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_SESSION_get_time.html>

       o   set_time

           Technically the same functionality as "SESSION_set_time".

            my $rv = Net::SSLeay::set_time($ses, $t);

       o   SESSION_set_timeout

           Sets the timeout value for session s in seconds to $t.

            my $rv = Net::SSLeay::SESSION_set_timeout($s, $t);
            # $s - value corresponding to openssl's SSL_SESSION structure
            # $t - timeout (in seconds)
            #
            # returns: 1 on success

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_SESSION_get_time.html>

       o   set_timeout

           Technically the same functionality as "SESSION_set_timeout".

            my $rv = Net::SSLeay::set_timeout($ses, $t);

       Low level API: SSL_CTX_* related functions

       NOTE: Please note that the function described in this chapter have
       "SSL_" part stripped from their original openssl names.

       o   CTX_add_client_CA

           Adds the CA name extracted from $cacert to the list of CAs sent to
           the client when requesting a client certificate for $ctx.

            my $rv = Net::SSLeay::CTX_add_client_CA($ctx, $cacert);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $cacert - value corresponding to openssl's X509 structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_client_CA_list.html>

       o   CTX_add_extra_chain_cert

           Adds the certificate $x509 to the certificate chain presented
           together with the certificate. Several certificates can be added
           one after the other.

            my $rv = Net::SSLeay::CTX_add_extra_chain_cert($ctx, $x509);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $x509 - value corresponding to openssl's X509 structure
            #
            # returns: 1 on success, check out the error stack to find out the reason for failure otherwise

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_add_extra_chain_cert.html>

       o   CTX_add_session

           Adds the session $ses to the context $ctx.

            my $rv = Net::SSLeay::CTX_add_session($ctx, $ses);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $ses - value corresponding to openssl's SSL_SESSION structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_add_session.html>

       o   CTX_callback_ctrl

           ??? (more info needed)

            my $rv = Net::SSLeay::CTX_callback_ctrl($ctx, $cmd, $fp);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $cmd - (integer) command id
            # $fp - (function pointer) ???
            #
            # returns: ???

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_ctrl.html>

       o   CTX_check_private_key

           Checks the consistency of a private key with the corresponding
           certificate loaded into $ctx.

            my $rv = Net::SSLeay::CTX_check_private_key($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   CTX_ctrl

           Internal handling function for SSL_CTX objects.

           BEWARE: openssl doc says: This function should never be called
           directly!

            my $rv = Net::SSLeay::CTX_ctrl($ctx, $cmd, $larg, $parg);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $cmd - (integer) command id
            # $larg - (integer) long ???
            # $parg - (string/pointer) ???
            #
            # returns: (long) result of given command ???

            #valid $cmd values
             1 - SSL_CTRL_NEED_TMP_RSA
             2 - SSL_CTRL_SET_TMP_RSA
             3 - SSL_CTRL_SET_TMP_DH
             4 - SSL_CTRL_SET_TMP_ECDH
             5 - SSL_CTRL_SET_TMP_RSA_CB
             6 - SSL_CTRL_SET_TMP_DH_CB
             7 - SSL_CTRL_SET_TMP_ECDH_CB
             8 - SSL_CTRL_GET_SESSION_REUSED
             9 - SSL_CTRL_GET_CLIENT_CERT_REQUEST
            10 - SSL_CTRL_GET_NUM_RENEGOTIATIONS
            11 - SSL_CTRL_CLEAR_NUM_RENEGOTIATIONS
            12 - SSL_CTRL_GET_TOTAL_RENEGOTIATIONS
            13 - SSL_CTRL_GET_FLAGS
            14 - SSL_CTRL_EXTRA_CHAIN_CERT
            15 - SSL_CTRL_SET_MSG_CALLBACK
            16 - SSL_CTRL_SET_MSG_CALLBACK_ARG
            17 - SSL_CTRL_SET_MTU
            20 - SSL_CTRL_SESS_NUMBER
            21 - SSL_CTRL_SESS_CONNECT
            22 - SSL_CTRL_SESS_CONNECT_GOOD
            23 - SSL_CTRL_SESS_CONNECT_RENEGOTIATE
            24 - SSL_CTRL_SESS_ACCEPT
            25 - SSL_CTRL_SESS_ACCEPT_GOOD
            26 - SSL_CTRL_SESS_ACCEPT_RENEGOTIATE
            27 - SSL_CTRL_SESS_HIT
            28 - SSL_CTRL_SESS_CB_HIT
            29 - SSL_CTRL_SESS_MISSES
            30 - SSL_CTRL_SESS_TIMEOUTS
            31 - SSL_CTRL_SESS_CACHE_FULL
            32 - SSL_CTRL_OPTIONS
            33 - SSL_CTRL_MODE
            40 - SSL_CTRL_GET_READ_AHEAD
            41 - SSL_CTRL_SET_READ_AHEAD
            42 - SSL_CTRL_SET_SESS_CACHE_SIZE
            43 - SSL_CTRL_GET_SESS_CACHE_SIZE
            44 - SSL_CTRL_SET_SESS_CACHE_MODE
            45 - SSL_CTRL_GET_SESS_CACHE_MODE
            50 - SSL_CTRL_GET_MAX_CERT_LIST
            51 - SSL_CTRL_SET_MAX_CERT_LIST
            52 - SSL_CTRL_SET_MAX_SEND_FRAGMENT
            53 - SSL_CTRL_SET_TLSEXT_SERVERNAME_CB
            54 - SSL_CTRL_SET_TLSEXT_SERVERNAME_ARG
            55 - SSL_CTRL_SET_TLSEXT_HOSTNAME
            56 - SSL_CTRL_SET_TLSEXT_DEBUG_CB
            57 - SSL_CTRL_SET_TLSEXT_DEBUG_ARG
            58 - SSL_CTRL_GET_TLSEXT_TICKET_KEYS
            59 - SSL_CTRL_SET_TLSEXT_TICKET_KEYS
            60 - SSL_CTRL_SET_TLSEXT_OPAQUE_PRF_INPUT
            61 - SSL_CTRL_SET_TLSEXT_OPAQUE_PRF_INPUT_CB
            62 - SSL_CTRL_SET_TLSEXT_OPAQUE_PRF_INPUT_CB_ARG
            63 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_CB
            64 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_CB_ARG
            65 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_TYPE
            66 - SSL_CTRL_GET_TLSEXT_STATUS_REQ_EXTS
            67 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_EXTS
            68 - SSL_CTRL_GET_TLSEXT_STATUS_REQ_IDS
            69 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_IDS
            70 - SSL_CTRL_GET_TLSEXT_STATUS_REQ_OCSP_RESP
            71 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_OCSP_RESP
            72 - SSL_CTRL_SET_TLSEXT_TICKET_KEY_CB
            73 - DTLS_CTRL_GET_TIMEOUT
            74 - DTLS_CTRL_HANDLE_TIMEOUT
            75 - DTLS_CTRL_LISTEN
            76 - SSL_CTRL_GET_RI_SUPPORT
            77 - SSL_CTRL_CLEAR_OPTIONS
            78 - SSL_CTRL_CLEAR_MODE

            82 - SSL_CTRL_GET_EXTRA_CHAIN_CERTS
            83 - SSL_CTRL_CLEAR_EXTRA_CHAIN_CERTS

            88 - SSL_CTRL_CHAIN
            89 - SSL_CTRL_CHAIN_CERT

            90 - SSL_CTRL_GET_CURVES
            91 - SSL_CTRL_SET_CURVES
            92 - SSL_CTRL_SET_CURVES_LIST
            93 - SSL_CTRL_GET_SHARED_CURVE
            94 - SSL_CTRL_SET_ECDH_AUTO
            97 - SSL_CTRL_SET_SIGALGS
            98 - SSL_CTRL_SET_SIGALGS_LIST
            99 - SSL_CTRL_CERT_FLAGS
            100 - SSL_CTRL_CLEAR_CERT_FLAGS
            101 - SSL_CTRL_SET_CLIENT_SIGALGS
            102 - SSL_CTRL_SET_CLIENT_SIGALGS_LIST
            103 - SSL_CTRL_GET_CLIENT_CERT_TYPES
            104 - SSL_CTRL_SET_CLIENT_CERT_TYPES
            105 - SSL_CTRL_BUILD_CERT_CHAIN
            106 - SSL_CTRL_SET_VERIFY_CERT_STORE
            107 - SSL_CTRL_SET_CHAIN_CERT_STORE
            108 - SSL_CTRL_GET_PEER_SIGNATURE_NID
            109 - SSL_CTRL_GET_SERVER_TMP_KEY
            110 - SSL_CTRL_GET_RAW_CIPHERLIST
            111 - SSL_CTRL_GET_EC_POINT_FORMATS
            112 - SSL_CTRL_GET_TLSA_RECORD
            113 - SSL_CTRL_SET_TLSA_RECORD
            114 - SSL_CTRL_PULL_TLSA_RECORD

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_ctrl.html>

       o   CTX_flush_sessions

           Causes a run through the session cache of $ctx to remove sessions
           expired at time $tm.

            Net::SSLeay::CTX_flush_sessions($ctx, $tm);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $tm - specifies the time which should be used for the expiration test (seconds since 1.1.1970)
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_flush_sessions.html>

       o   CTX_free

           Free an allocated SSL_CTX object.

            Net::SSLeay::CTX_free($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_free.html>

       o   CTX_get_app_data

           Can be used to get application defined value/data.

            my $rv = Net::SSLeay::CTX_get_app_data($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: string/buffer/pointer ???

       o   CTX_set_app_data

           Can be used to set some application defined value/data.

            my $rv = Net::SSLeay::CTX_set_app_data($ctx, $arg);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $arg - (string/buffer/pointer ???) data
            #
            # returns: ???

       o   CTX_get_cert_store

           Returns the current certificate verification storage.

            my $rv = Net::SSLeay::CTX_get_cert_store($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: value corresponding to openssl's X509_STORE structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_cert_store.html>

       o   CTX_get_client_CA_list

           Returns the list of client CAs explicitly set for $ctx using
           "CTX_set_client_CA_list".

            my $rv = Net::SSLeay::CTX_get_client_CA_list($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: value corresponding to openssl's X509_NAME_STACK structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_client_CA_list.html>

       o   CTX_get_ex_data

           Is used to retrieve the information for index $idx from $ctx.

            my $rv = Net::SSLeay::CTX_get_ex_data($ssl, $idx);
            # $ssl - value corresponding to openssl's SSL_CTX structure
            # $idx - (integer) index for application specific data
            #
            # returns: pointer to ???

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_get_ex_new_index.html>

       o   CTX_get_ex_new_index

           Is used to register a new index for application specific data.

            my $rv = Net::SSLeay::CTX_get_ex_new_index($argl, $argp, $new_func, $dup_func, $free_func);
            # $argl - (long) ???
            # $argp - (pointer) ???
            # $new_func - function pointer ??? (CRYPTO_EX_new *)
            # $dup_func - function pointer ??? (CRYPTO_EX_dup *)
            # $free_func - function pointer ??? (CRYPTO_EX_free *)
            #
            # returns: (integer) ???

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_get_ex_new_index.html>

       o   CTX_get_mode

           Returns the mode set for ctx.

            my $rv = Net::SSLeay::CTX_get_mode($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: mode (bitmask)

            #to decode the return value (bitmask) use:
            0x00000001 corresponds to SSL_MODE_ENABLE_PARTIAL_WRITE
            0x00000002 corresponds to SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER
            0x00000004 corresponds to SSL_MODE_AUTO_RETRY
            0x00000008 corresponds to SSL_MODE_NO_AUTO_CHAIN
            0x00000010 corresponds to SSL_MODE_RELEASE_BUFFERS
            (note: some of the bits might not be supported by older openssl versions)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_mode.html>

       o   CTX_set_mode

           Adds the mode set via bitmask in $mode to $ctx. Options already set
           before are not cleared.

            my $rv = Net::SSLeay::CTX_set_mode($ctx, $mode);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $mode - mode bitmask
            #
            # returns: the new mode bitmask after adding $mode

           For bitmask details see "CTX_get_mode" (above).

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_mode.html>

       o   CTX_get_options

           Returns the options (bitmask) set for $ctx.

            my $rv = Net::SSLeay::CTX_get_options($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: options (bitmask)

            #to decode the return value (bitmask) use:
            0x00000001 corresponds to SSL_OP_MICROSOFT_SESS_ID_BUG
            0x00000002 corresponds to SSL_OP_NETSCAPE_CHALLENGE_BUG
            0x00000004 corresponds to SSL_OP_LEGACY_SERVER_CONNECT
            0x00000008 corresponds to SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
            0x00000010 corresponds to SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
            0x00000020 corresponds to SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
            0x00000040 corresponds to SSL_OP_MSIE_SSLV2_RSA_PADDING
            0x00000080 corresponds to SSL_OP_SSLEAY_080_CLIENT_DH_BUG
            0x00000100 corresponds to SSL_OP_TLS_D5_BUG
            0x00000200 corresponds to SSL_OP_TLS_BLOCK_PADDING_BUG
            0x00000800 corresponds to SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
            0x80000FFF corresponds to SSL_OP_ALL
            0x00001000 corresponds to SSL_OP_NO_QUERY_MTU
            0x00002000 corresponds to SSL_OP_COOKIE_EXCHANGE
            0x00004000 corresponds to SSL_OP_NO_TICKET
            0x00008000 corresponds to SSL_OP_CISCO_ANYCONNECT
            0x00010000 corresponds to SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
            0x00020000 corresponds to SSL_OP_NO_COMPRESSION
            0x00040000 corresponds to SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
            0x00080000 corresponds to SSL_OP_SINGLE_ECDH_USE
            0x00100000 corresponds to SSL_OP_SINGLE_DH_USE
            0x00200000 corresponds to SSL_OP_EPHEMERAL_RSA
            0x00400000 corresponds to SSL_OP_CIPHER_SERVER_PREFERENCE
            0x00800000 corresponds to SSL_OP_TLS_ROLLBACK_BUG
            0x01000000 corresponds to SSL_OP_NO_SSLv2
            0x02000000 corresponds to SSL_OP_NO_SSLv3
            0x04000000 corresponds to SSL_OP_NO_TLSv1
            0x08000000 corresponds to SSL_OP_PKCS1_CHECK_1
            0x10000000 corresponds to SSL_OP_PKCS1_CHECK_2
            0x20000000 corresponds to SSL_OP_NETSCAPE_CA_DN_BUG
            0x40000000 corresponds to SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
            0x80000000 corresponds to SSL_OP_CRYPTOPRO_TLSEXT_BUG
            (note: some of the bits might not be supported by older openssl versions)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_options.html>

       o   CTX_set_options

           Adds the options set via bitmask in $options to ctx. Options
           already set before are not cleared.

            Net::SSLeay::CTX_set_options($ctx, $options);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $options - options bitmask
            #
            # returns: the new options bitmask after adding $options

           For bitmask details see "CTX_get_options" (above).

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_options.html>

       o   CTX_get_quiet_shutdown

           Returns the 'quiet shutdown' setting of $ctx.

            my $rv = Net::SSLeay::CTX_get_quiet_shutdown($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: (integer) the current setting

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_quiet_shutdown.html>

       o   CTX_get_read_ahead

            my $rv = Net::SSLeay::CTX_get_read_ahead($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: (integer) read_ahead value

       o   CTX_get_session_cache_mode

           Returns the currently used cache mode (bitmask).

            my $rv = Net::SSLeay::CTX_get_session_cache_mode($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: mode (bitmask)

            #to decode the return value (bitmask) use:
            0x0000 corresponds to SSL_SESS_CACHE_OFF
            0x0001 corresponds to SSL_SESS_CACHE_CLIENT
            0x0002 corresponds to SSL_SESS_CACHE_SERVER
            0x0080 corresponds to SSL_SESS_CACHE_NO_AUTO_CLEAR
            0x0100 corresponds to SSL_SESS_CACHE_NO_INTERNAL_LOOKUP
            0x0200 corresponds to SSL_SESS_CACHE_NO_INTERNAL_STORE
            (note: some of the bits might not be supported by older openssl versions)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_session_cache_mode.html>

       o   CTX_set_session_cache_mode

           Enables/disables session caching by setting the operational mode
           for $ctx to $mode.

            my $rv = Net::SSLeay::CTX_set_session_cache_mode($ctx, $mode);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $mode - mode (bitmask)
            #
            # returns: previously set cache mode

           For bitmask details see "CTX_get_session_cache_mode" (above).

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_session_cache_mode.html>

       o   CTX_get_timeout

           Returns the currently set timeout value for $ctx.

            my $rv = Net::SSLeay::CTX_get_timeout($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: timeout in seconds

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_timeout.html>

       o   CTX_get_verify_depth

           Returns the verification depth limit currently set in $ctx. If no
           limit has been explicitly set, -1 is returned and the default value
           will be used.",

            my $rv = Net::SSLeay::CTX_get_verify_depth($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: depth limit currently set in $ctx, -1 if no limit has been explicitly set

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_get_verify_mode.html>

       o   CTX_get_verify_mode

           Returns the verification mode (bitmask) currently set in $ctx.

            my $rv = Net::SSLeay::CTX_get_verify_mode($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: mode (bitmask)

            #to decode the return value (bitmask) use:
            0x00 corresponds to SSL_VERIFY_NONE
            0x01 corresponds to SSL_VERIFY_PEER
            0x02 corresponds to SSL_VERIFY_FAIL_IF_NO_PEER_CERT
            0x04 corresponds to SSL_VERIFY_CLIENT_ONCE
            (note: some of the bits might not be supported by older openssl versions)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_get_verify_mode.html>

       o   CTX_set_verify

           Sets the verification flags for $ctx to be $mode and specifies the
           verify_callback function to be used.

            Net::SSLeay::CTX_set_verify($ctx, $mode, $callback);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $mode - mode (bitmask)
            # $callback - [optional] reference to perl callback function
            #
            # returns: no return value

           For bitmask details see "CTX_get_verify_mode" (above).

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_verify.html>

       o   CTX_load_verify_locations

           Specifies the locations for $ctx, at which CA certificates for
           verification purposes are located. The certificates available via
           $CAfile and $CApath are trusted.

            my $rv = Net::SSLeay::CTX_load_verify_locations($ctx, $CAfile, $CApath);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $CAfile - (string) file of CA certificates in PEM format, the file can contain several CA certificates (or '')
            # $CApath - (string) directory containing CA certificates in PEM format (or '')
            #
            # returns: 1 on success, 0 on failure (check the error stack to find out the reason)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_load_verify_locations.html>

       o   CTX_need_tmp_RSA

           Return the result of
           "SSL_CTX_ctrl(ctx,SSL_CTRL_NEED_TMP_RSA,0,NULL)"

            my $rv = Net::SSLeay::CTX_need_tmp_RSA($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: result of SSL_CTRL_NEED_TMP_RSA command

           Not available with OpenSSL 1.1 and later.

       o   CTX_new

           The same as "CTX_v23_new"

            my $rv = Net::SSLeay::CTX_new();
            #
            # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_new.html>

           Not available with OpenSSL 1.1 and later.

       o   CTX_v2_new

           Creates a new SSL_CTX object - based on SSLv2_method() - as
           framework to establish TLS/SSL enabled connections.

            my $rv = Net::SSLeay::CTX_v2_new();
            #
            # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

       o   CTX_v23_new

           Creates a new SSL_CTX object - based on SSLv23_method() - as
           framework to establish TLS/SSL enabled connections.

            my $rv = Net::SSLeay::CTX_v23_new();
            #
            # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

       o   CTX_v3_new

           Creates a new SSL_CTX object - based on SSLv3_method() - as
           framework to establish TLS/SSL enabled connections.

            my $rv = Net::SSLeay::CTX_v3_new();
            #
            # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

       o   CTX_tlsv1_new

           Creates a new SSL_CTX object - based on TLSv1_method() - as
           framework to establish TLS/SSL enabled connections.

            my $rv = Net::SSLeay::CTX_tlsv1_new();
            #
            # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

       o   CTX_tlsv1_1_new

           Creates a new SSL_CTX object - based on TLSv1_1_method() - as
           framework to establish TLS/SSL enabled connections. Only available
           where supported by the underlying openssl.

            my $rv = Net::SSLeay::CTX_tlsv1_1_new();
            #
            # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

       o   CTX_tlsv1_2_new

           Creates a new SSL_CTX object - based on TLSv1_2_method() - as
           framework to establish TLS/SSL enabled connections. Only available
           where supported by the underlying openssl.

            my $rv = Net::SSLeay::CTX_tlsv1_2_new();
            #
            # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

       o   CTX_new_with_method

           Creates a new SSL_CTX object based on $meth method

            my $rv = Net::SSLeay::CTX_new_with_method($meth);
            # $meth - value corresponding to openssl's SSL_METHOD structure
            #
            # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

            #example
            my $ctx = Net::SSLeay::CTX_new_with_method(&Net::SSLeay::TLSv1_method);

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_new.html>

       o   CTX_remove_session

           Removes the session $ses from the context $ctx.

            my $rv = Net::SSLeay::CTX_remove_session($ctx, $ses);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $ses - value corresponding to openssl's SSL_SESSION structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_add_session.html>

       o   CTX_sess_accept

            my $rv = Net::SSLeay::CTX_sess_accept($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: number of started SSL/TLS handshakes in server mode

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

       o   CTX_sess_accept_good

            my $rv = Net::SSLeay::CTX_sess_accept_good($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: number of successfully established SSL/TLS sessions in server mode

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

       o   CTX_sess_accept_renegotiate

            my $rv = Net::SSLeay::CTX_sess_accept_renegotiate($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: number of start renegotiations in server mode

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

       o   CTX_sess_cache_full

            my $rv = Net::SSLeay::CTX_sess_cache_full($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: number of sessions that were removed because the maximum session cache size was exceeded

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

       o   CTX_sess_cb_hits

            my $rv = Net::SSLeay::CTX_sess_cb_hits($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: number of successfully retrieved sessions from the external session cache in server mode

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

       o   CTX_sess_connect

            my $rv = Net::SSLeay::CTX_sess_connect($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: number of started SSL/TLS handshakes in client mode

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

       o   CTX_sess_connect_good

            my $rv = Net::SSLeay::CTX_sess_connect_good($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: number of successfully established SSL/TLS sessions in client mode

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

       o   CTX_sess_connect_renegotiate

            my $rv = Net::SSLeay::CTX_sess_connect_renegotiate($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: number of start renegotiations in client mode

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

       o   CTX_sess_get_cache_size

           Returns the currently valid session cache size.

            my $rv = Net::SSLeay::CTX_sess_get_cache_size($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: current size

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_sess_set_cache_size.html>

       o   CTX_sess_hits

            my $rv = Net::SSLeay::CTX_sess_hits($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: number of successfully reused sessions

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

       o   CTX_sess_misses

            my $rv = Net::SSLeay::CTX_sess_misses($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: number of sessions proposed by clients that were not found in the internal session cache in server mode

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

       o   CTX_sess_number

            my $rv = Net::SSLeay::CTX_sess_number($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: current number of sessions in the internal session cache

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

       o   CTX_sess_set_cache_size

           Sets the size of the internal session cache of context $ctx to
           $size.

            Net::SSLeay::CTX_sess_set_cache_size($ctx, $size);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $size - cache size (0 = unlimited)
            #
            # returns: previously valid size

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_sess_set_cache_size.html>

       o   CTX_sess_timeouts

           Returns the number of sessions proposed by clients and either found
           in the internal or external session cache in server mode, but that
           were invalid due to timeout. These sessions are not included in the
           SSL_CTX_sess_hits count.

            my $rv = Net::SSLeay::CTX_sess_timeouts($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: number of sessions

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

       o   CTX_sessions

           Returns a pointer to the lhash databases containing the internal
           session cache for ctx.

            my $rv = Net::SSLeay::CTX_sessions($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: value corresponding to openssl's LHASH structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_sessions.html>

       o   CTX_set1_param

           Applies X509 verification parameters $vpm on $ctx

            my $rv = Net::SSLeay::CTX_set1_param($ctx, $vpm);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $vpm - value corresponding to openssl's X509_VERIFY_PARAM structure
            #
            # returns: 1 on success, 0 on failure

       o   CTX_set_cert_store

           Sets/replaces the certificate verification storage of $ctx to/with
           $store.

            Net::SSLeay::CTX_set_cert_store($ctx, $store);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $store - value corresponding to openssl's X509_STORE structure
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_cert_store.html>

       o   CTX_set_cert_verify_callback

           Sets the verification callback function for $ctx. SSL objects that
           are created from $ctx inherit the setting valid at the time when
           "Net::SSLeay::new($ctx)" is called.

            Net::SSLeay::CTX_set_cert_verify_callback($ctx, $func, $data);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $func - perl reference to callback function
            # $data - [optional] data that will be passed to callback function when invoked
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_cert_verify_callback.html>

       o   CTX_set_cipher_list

           Sets the list of available ciphers for $ctx using the control
           string $str.  The list of ciphers is inherited by all ssl objects
           created from $ctx.

            my $rv = Net::SSLeay::CTX_set_cipher_list($s, $str);
            # $s - value corresponding to openssl's SSL_CTX structure
            # $str - (string) cipher list e.g. '3DES:+RSA'
            #
            # returns: 1 if any cipher could be selected and 0 on complete failure

           The format of $str is described in
           <http://www.openssl.org/docs/apps/ciphers.html>

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_cipher_list.html>

       o   CTX_set_client_CA_list

           Sets the list of CAs sent to the client when requesting a client
           certificate for $ctx.

            Net::SSLeay::CTX_set_client_CA_list($ctx, $list);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $list - value corresponding to openssl's X509_NAME_STACK structure
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_client_CA_list.html>

       o   CTX_set_default_passwd_cb

           Sets the default password callback called when loading/storing a
           PEM certificate with encryption.

            Net::SSLeay::CTX_set_default_passwd_cb($ctx, $func);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $func - perl reference to callback function
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_default_passwd_cb.html>

       o   CTX_set_default_passwd_cb_userdata

           Sets a pointer to userdata which will be provided to the password
           callback on invocation.

            Net::SSLeay::CTX_set_default_passwd_cb_userdata($ctx, $userdata);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $userdata - data that will be passed to callback function when invoked
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_default_passwd_cb.html>

       o   CTX_set_default_verify_paths

           ??? (more info needed)

            my $rv = Net::SSLeay::CTX_set_default_verify_paths($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: 1 on success, 0 on failure

       o   CTX_set_ex_data

           Is used to store application data at $data for $idx into the $ctx
           object.

            my $rv = Net::SSLeay::CTX_set_ex_data($ssl, $idx, $data);
            # $ssl - value corresponding to openssl's SSL_CTX structure
            # $idx - (integer) ???
            # $data - (pointer) ???
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_get_ex_new_index.html>

       o   CTX_set_purpose

            my $rv = Net::SSLeay::CTX_set_purpose($s, $purpose);
            # $s - value corresponding to openssl's SSL_CTX structure
            # $purpose - (integer) purpose identifier
            #
            # returns: 1 on success, 0 on failure

            #avainable purpose identifier
            1 - X509_PURPOSE_SSL_CLIENT
            2 - X509_PURPOSE_SSL_SERVER
            3 - X509_PURPOSE_NS_SSL_SERVER
            4 - X509_PURPOSE_SMIME_SIGN
            5 - X509_PURPOSE_SMIME_ENCRYPT
            6 - X509_PURPOSE_CRL_SIGN
            7 - X509_PURPOSE_ANY
            8 - X509_PURPOSE_OCSP_HELPER
            9 - X509_PURPOSE_TIMESTAMP_SIGN

            #or use corresponding constants
            $purpose = &Net::SSLeay::X509_PURPOSE_SSL_CLIENT;
            ...
            $purpose = &Net::SSLeay::X509_PURPOSE_TIMESTAMP_SIGN;

       o   CTX_set_quiet_shutdown

           Sets the 'quiet shutdown' flag for $ctx to be mode. SSL objects
           created from $ctx inherit the mode valid at the time
           "Net::SSLeay::new($ctx)" is called.

            Net::SSLeay::CTX_set_quiet_shutdown($ctx, $mode);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $mode - 0 or 1
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_quiet_shutdown.html>

       o   CTX_set_read_ahead

            my $rv = Net::SSLeay::CTX_set_read_ahead($ctx, $val);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $val - read_ahead value to be set
            #
            # returns: the original read_ahead value

       o   CTX_set_session_id_context

           Sets the context $sid_ctx of length $sid_ctx_len within which a
           session can be reused for the $ctx object.

            my $rv = Net::SSLeay::CTX_set_session_id_context($ctx, $sid_ctx, $sid_ctx_len);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $sid_ctx - data buffer
            # $sid_ctx_len - length of data in $sid_ctx
            #
            # returns: 1 on success, 0 on failure (the error is logged to the error stack)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_session_id_context.html>

       o   CTX_set_ssl_version

           Sets a new default TLS/SSL method for SSL objects newly created
           from this $ctx.  SSL objects already created with
           "Net::SSLeay::new($ctx)" are not affected, except when
           "Net::SSLeay:clear($ssl)" is being called.

            my $rv = Net::SSLeay::CTX_set_ssl_version($ctx, $meth);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $meth - value corresponding to openssl's SSL_METHOD structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_ssl_version.html>

       o   CTX_set_timeout

           Sets the timeout for newly created sessions for $ctx to $t. The
           timeout value $t must be given in seconds.

            my $rv = Net::SSLeay::CTX_set_timeout($ctx, $t);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $t - timeout in seconds
            #
            # returns: previously set timeout value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_timeout.html>

       o   CTX_set_tmp_dh

           Sets DH parameters to be used to be $dh. The key is inherited by
           all ssl objects created from $ctx.

            my $rv = Net::SSLeay::CTX_set_tmp_dh($ctx, $dh);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $dh - value corresponding to openssl's DH structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_dh_callback.html>

       o   CTX_set_tmp_dh_callback

           Sets the callback function for $ctx to be used when a DH parameters
           are required to $tmp_dh_callback.

            Net::SSLeay::CTX_set_tmp_dh_callback($ctx, $tmp_dh_callback);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # tmp_dh_callback - (function pointer) ???
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_dh_callback.html>

       o   CTX_set_tmp_rsa

           Sets the temporary/ephemeral RSA key to be used to be $rsa.

            my $rv = Net::SSLeay::CTX_set_tmp_rsa($ctx, $rsa);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $rsa - value corresponding to openssl's RSA structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_rsa_callback.html>

           Not available with OpenSSL 1.1 and later.

       o   CTX_set_tmp_rsa_callback

           Sets the callback function for ctx to be used when a
           temporary/ephemeral RSA key is required to $tmp_rsa_callback.

           ??? (does this function really work?)

            Net::SSLeay::CTX_set_tmp_rsa_callback($ctx, $tmp_rsa_callback);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $tmp_rsa_callback - (function pointer) ???
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_rsa_callback.html>

           Not available with OpenSSL 1.1 and later.

       o   CTX_set_trust

            my $rv = Net::SSLeay::CTX_set_trust($s, $trust);
            # $s - value corresponding to openssl's SSL_CTX structure
            # $trust - (integer) trust identifier
            #
            # returns: the original value

            #available trust identifiers
            1 - X509_TRUST_COMPAT
            2 - X509_TRUST_SSL_CLIENT
            3 - X509_TRUST_SSL_SERVER
            4 - X509_TRUST_EMAIL
            5 - X509_TRUST_OBJECT_SIGN
            6 - X509_TRUST_OCSP_SIGN
            7 - X509_TRUST_OCSP_REQUEST
            8 - X509_TRUST_TSA

            #or use corresponding constants
            $trust = &Net::SSLeay::X509_TRUST_COMPAT;
            ...
            $trust = &Net::SSLeay::X509_TRUST_TSA;

       o   CTX_set_verify_depth

           Sets the maximum depth for the certificate chain verification that
           shall be allowed for ctx.

            Net::SSLeay::CTX_set_verify_depth($ctx, $depth);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $depth - max. depth
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_verify.html>

       o   CTX_use_PKCS12_file

           Adds the certificate and private key from PKCS12 file $p12filename
           to $ctx.

            my $rv = Net::SSLeay::CTX_use_PKCS12_file($ctx, $p12filename, $password);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $p12filename - (string) filename
            # $password - (string) password to decrypt private key
            #
            # returns: 1 on success, 0 on failure

       o   CTX_use_PrivateKey

           Adds the private key $pkey to $ctx.

            my $rv = Net::SSLeay::CTX_use_PrivateKey($ctx, $pkey);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $pkey - value corresponding to openssl's EVP_PKEY structure
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   CTX_use_PrivateKey_file

           Adds the first private key found in $file to $ctx.

            my $rv = Net::SSLeay::CTX_use_PrivateKey_file($ctx, $file, $type);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $file - (string) file name
            # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   CTX_use_RSAPrivateKey

           Adds the RSA private key $rsa to $ctx.

            my $rv = Net::SSLeay::CTX_use_RSAPrivateKey($ctx, $rsa);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $rsa - value corresponding to openssl's RSA structure
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   CTX_use_RSAPrivateKey_file

           Adds the first RSA private key found in $file to $ctx.

            my $rv = Net::SSLeay::CTX_use_RSAPrivateKey_file($ctx, $file, $type);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $file - (string) file name
            # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

       o   CTX_use_certificate

           Loads the certificate $x into $ctx

            my $rv = Net::SSLeay::CTX_use_certificate($ctx, $x);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   CTX_use_certificate_chain_file

           Loads a certificate chain from $file into $ctx. The certificates
           must be in PEM format and must be sorted starting with the
           subject's certificate (actual client or server certificate),
           followed by intermediate CA certificates if applicable, and ending
           at the highest level (root) CA.

            my $rv = Net::SSLeay::CTX_use_certificate_chain_file($ctx, $file);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $file - (string) file name
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   CTX_use_certificate_file

           Loads the first certificate stored in $file into $ctx.

            my $rv = Net::SSLeay::CTX_use_certificate_file($ctx, $file, $type);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $file - (string) file name
            # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       Low level API: SSL_* related functions

       NOTE: Please note that the function described in this chapter have
       "SSL_" part stripped from their original openssl names.

       o   new

           Creates a new SSL structure which is needed to hold the data for a
           TLS/SSL connection.  The new structure inherits the settings of the
           underlying context $ctx: connection method (SSLv2/v3/TLSv1),
           options, verification settings, timeout settings.

            my $rv = Net::SSLeay::new($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: value corresponding to openssl's SSL structure (0 on failure)

           Check openssl doc <http://www.openssl.org/docs/ssl/SSL_new.html>

       o   accept

           Waits for a TLS/SSL client to initiate the TLS/SSL handshake. The
           communication channel must already have been set and assigned to
           the ssl by setting an underlying BIO.

            my $rv = Net::SSLeay::accept($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: 1 = success, 0 = handshake not successful, <0 = fatal error during handshake

           Check openssl doc <http://www.openssl.org/docs/ssl/SSL_accept.html>

       o   add_client_CA

           Adds the CA name extracted from cacert to the list of CAs sent to
           the client when requesting a client certificate for the chosen ssl,
           overriding the setting valid for ssl's SSL_CTX object.

            my $rv = Net::SSLeay::add_client_CA($ssl, $x);
            # $ssl - value corresponding to openssl's SSL structure
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_client_CA_list.html>

       o   callback_ctrl

           ??? (more info needed)

            my $rv = Net::SSLeay::callback_ctrl($ssl, $cmd, $fp);
            # $ssl - value corresponding to openssl's SSL structure
            # $cmd - (integer) command id
            # $fp - (function pointer) ???
            #
            # returns: ???

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_ctrl.html>

       o   check_private_key

           Checks the consistency of a private key with the corresponding
           certificate loaded into $ssl

            my $rv = Net::SSLeay::check_private_key($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   clear

           Reset SSL object to allow another connection.

            Net::SSLeay::clear($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: no return value

           Check openssl doc <http://www.openssl.org/docs/ssl/SSL_clear.html>

       o   connect

           Initiate the TLS/SSL handshake with an TLS/SSL server.

            my $rv = Net::SSLeay::connect($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: 1 = success, 0 = handshake not successful, <0 = fatal error during handshake

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_connect.html>

       o   copy_session_id

           Copies the session structure fro $from to $to (+ also the private
           key and certificate associated with $from).

            Net::SSLeay::copy_session_id($to, $from);
            # $to - value corresponding to openssl's SSL structure
            # $from - value corresponding to openssl's SSL structure
            #
            # returns: no return value

       o   ctrl

           Internal handling function for SSL objects.

           BEWARE: openssl doc says: This function should never be called
           directly!

            my $rv = Net::SSLeay::ctrl($ssl, $cmd, $larg, $parg);
            # $ssl - value corresponding to openssl's SSL structure
            # $cmd - (integer) command id
            # $larg - (integer) long ???
            # $parg - (string/pointer) ???
            #
            # returns: (long) result of given command ???

           For more details about valid $cmd values check "CTX_ctrl".

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_ctrl.html>

       o   do_handshake

           Will wait for a SSL/TLS handshake to take place. If the connection
           is in client mode, the handshake will be started. The handshake
           routines may have to be explicitly set in advance using either
           SSL_set_connect_state or SSL_set_accept_state(3).

            my $rv = Net::SSLeay::do_handshake($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: 1 = success, 0 = handshake not successful, <0 = fatal error during handshake

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_do_handshake.html>

       o   dup

           Returns a duplicate of $ssl.

            my $rv = Net::SSLeay::dup($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: value corresponding to openssl's SSL structure (0 on failure)

       o   free

           Free an allocated SSL structure.

            Net::SSLeay::free($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: no return value

           Check openssl doc <http://www.openssl.org/docs/ssl/SSL_free.html>

       o   get_SSL_CTX

           Returns a pointer to the SSL_CTX object, from which $ssl was
           created with Net::SSLeay::new.

            my $rv = Net::SSLeay::get_SSL_CTX($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_SSL_CTX.html>

       o   set_SSL_CTX

           Sets the SSL_CTX the corresponds to an SSL session.

            my $the_ssl_ctx = Net::SSLeay::set_SSL_CTX($ssl, $ssl_ctx);
            # $ssl - value corresponding to openssl's SSL structure
            # $ssl_ctx - Change the ssl object to the given ssl_ctx
            #
            # returns - the ssl_ctx

       o   get_app_data

           Can be used to get application defined value/data.

            my $rv = Net::SSLeay::get_app_data($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: string/buffer/pointer ???

       o   set_app_data

           Can be used to set some application defined value/data.

            my $rv = Net::SSLeay::set_app_data($ssl, $arg);
            # $ssl - value corresponding to openssl's SSL structure
            # $arg - (string/buffer/pointer ???) data
            #
            # returns: ???

       o   get_certificate

           Gets X509 certificate from an established SSL connection.

            my $rv = Net::SSLeay::get_certificate($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: value corresponding to openssl's X509 structure (0 on failure)

       o   get_cipher

           Obtains the name of the currently used cipher.

            my $rv = Net::SSLeay::get_cipher($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: (string) cipher name e.g. 'DHE-RSA-AES256-SHA' or '', when no session has been established.

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_current_cipher.html>

       o   get_cipher_bits

           Obtain the number of secret/algorithm bits used.

            my $rv = Net::SSLeay::get_cipher_bits($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: number of secret bits used by current cipher

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_current_cipher.html> and
           <http://www.openssl.org/docs/ssl/SSL_CIPHER_get_name.html>

       o   get_cipher_list

           Returns the name (string) of the SSL_CIPHER listed for $ssl with
           priority $n.

            my $rv = Net::SSLeay::get_cipher_list($ssl, $n);
            # $ssl - value corresponding to openssl's SSL structure
            # $n - (integer) priority
            #
            # returns: (string) cipher name e.g. 'EDH-DSS-DES-CBC3-SHA' or '' in case of error

           Call Net::SSLeay::get_cipher_list with priority starting from 0 to
           obtain the sorted list of available ciphers, until '' is returned:

            my $priority = 0;
            while (my $c = Net::SSLeay::get_cipher_list($ssl, $priority)) {
              print "cipher[$priority] = $c\n";
              $priority++;
            }

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_ciphers.html>

       o   get_client_CA_list

           Returns the list of client CAs explicitly set for $ssl using
           "Net::SSleay::set_client_CA_list" or $ssl's SSL_CTX object with
           "Net::SSLeay::CTX_set_client_CA_list", when in server mode.

           In client mode, returns the list of client CAs sent from the
           server, if any.

            my $rv = Net::SSLeay::get_client_CA_list($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: value corresponding to openssl's STACK_OF(X509_NAME) structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_client_CA_list.html>

       o   get_current_cipher

           Returns the cipher actually used.

            my $rv = Net::SSLeay::get_current_cipher($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: value corresponding to openssl's SSL_CIPHER structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_current_cipher.html>

       o   get_default_timeout

           Returns the default timeout value assigned to SSL_SESSION objects
           negotiated for the protocol valid for $ssl.

            my $rv = Net::SSLeay::get_default_timeout($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: (long) timeout in seconds

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_default_timeout.html>

       o   get_error

           Returns a result code for a preceding call to "connect", "accept",
           "do_handshake", "read", "peek" or "write" on $ssl.

            my $rv = Net::SSLeay::get_error($ssl, $ret);
            # $ssl - value corresponding to openssl's SSL structure
            # $ret - return value of preceding TLS/SSL I/O operation
            #
            # returns: result code, which is one of the following values:
            #  0 - SSL_ERROR_NONE
            #  1 - SSL_ERROR_SSL
            #  2 - SSL_ERROR_WANT_READ
            #  3 - SSL_ERROR_WANT_WRITE
            #  4 - SSL_ERROR_WANT_X509_LOOKUP
            #  5 - SSL_ERROR_SYSCALL
            #  6 - SSL_ERROR_ZERO_RETURN
            #  7 - SSL_ERROR_WANT_CONNECT
            #  8 - SSL_ERROR_WANT_ACCEPT

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_error.html>

       o   get_ex_data

           Is used to retrieve the information for $idx from $ssl.

            my $rv = Net::SSLeay::get_ex_data($ssl, $idx);
            # $ssl - value corresponding to openssl's SSL structure
            # $idx - (integer) index for application specific data
            #
            # returns: pointer to ???

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_ex_new_index.html>

       o   set_ex_data

           Is used to store application data at $data for $idx into the $ssl
           object.

            my $rv = Net::SSLeay::set_ex_data($ssl, $idx, $data);
            # $ssl - value corresponding to openssl's SSL structure
            # $idx - (integer) ???
            # $data - (pointer) ???
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_ex_new_index.html>

       o   get_ex_new_index

           Is used to register a new index for application specific data.

            my $rv = Net::SSLeay::get_ex_new_index($argl, $argp, $new_func, $dup_func, $free_func);
            # $argl - (long) ???
            # $argp - (pointer) ???
            # $new_func - function pointer ??? (CRYPTO_EX_new *)
            # $dup_func - function pointer ??? (CRYPTO_EX_dup *)
            # $free_func - function pointer ??? (CRYPTO_EX_free *)
            #
            # returns: (integer) ???

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_ex_new_index.html>

       o   get_fd

           Returns the file descriptor which is linked to $ssl.

            my $rv = Net::SSLeay::get_fd($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: file descriptor (>=0) or -1 on failure

           Check openssl doc <http://www.openssl.org/docs/ssl/SSL_get_fd.html>

       o   get_finished

           Obtains the latest 'Finished' message sent to the peer. Return
           value is zero if there's been no Finished message yet. Default
           count is 2*EVP_MAX_MD_SIZE that is long enough for all possible
           Finish messages. If you supply a non-default count, the resulting
           return value may be longer than returned buf's length.

            my $rv = Net::SSLeay::get_finished($ssl, $buf, $count);
            # $ssl - value corresponding to openssl's SSL structure
            # $buf - buffer where the returned data will be stored
            # $count - [optional] max size of return data - default is 2*EVP_MAX_MD_SIZE
            #
            # returns: length of latest Finished message

       o   get_peer_finished

           Obtains the latest 'Finished' message expected from the peer.
           Parameters and return value are similar to get_finished().

            my $rv = Net::SSLeay::get_peer_finished($ssl, $buf, $count);
            # $ssl - value corresponding to openssl's SSL structure
            # $buf - buffer where the returned data will be stored
            # $count - [optional] max size of return data - default is 2*EVP_MAX_MD_SIZE
            #
            # returns: length of latest Finished message

       o   get_keyblock_size

           Gets the length of the TLS keyblock.

           NOTE: Does not exactly correspond to any low level API function.

            my $rv = Net::SSLeay::get_keyblock_size($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: keyblock size, -1 on error

       o   get_mode

           Returns the mode (bitmask) set for $ssl.

            my $rv = Net::SSLeay::get_mode($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: mode (bitmask)

           To decode the return value (bitmask) see documentation for
           "CTX_get_mode".

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_mode.html>

       o   set_mode

           Adds the mode set via bitmask in $mode to $ssl. Options already set
           before are not cleared.

            my $rv = Net::SSLeay::set_mode($ssl, $mode);
            # $ssl - value corresponding to openssl's SSL structure
            # $mode - mode (bitmask)
            #
            # returns: the new mode bitmask after adding $mode

           For $mode bitmask details see "CTX_get_mode".

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_mode.html>

       o   get_options

           Returns the options (bitmask) set for $ssl.

            my $rv = Net::SSLeay::get_options($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: options (bitmask)

           To decode the return value (bitmask) see documentation for
           "CTX_get_options".

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_options.html>

       o   set_options

           Adds the options set via bitmask in $options to $ssl. Options
           already set before are not cleared!

            Net::SSLeay::set_options($ssl, $options);
            # $ssl - value corresponding to openssl's SSL structure
            # $options - options (bitmask)
            #
            # returns: the new options bitmask after adding $options

           For $options bitmask details see "CTX_get_options".

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_options.html>

       o   get_peer_certificate

           Get the X509 certificate of the peer.

            my $rv = Net::SSLeay::get_peer_certificate($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: value corresponding to openssl's X509 structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_peer_certificate.html>

       o   get_peer_cert_chain

           Get the certificate chain of the peer as an array of X509
           structures.

            my @rv = Net::SSLeay::get_peer_cert_chain($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: list of X509 structures

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_peer_certificate.html>

       o   get_quiet_shutdown

           Returns the 'quiet shutdown' setting of ssl.

            my $rv = Net::SSLeay::get_quiet_shutdown($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: (integer) current 'quiet shutdown' value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_quiet_shutdown.html>

       o   get_rbio

           Get 'read' BIO linked to an SSL object $ssl.

            my $rv = Net::SSLeay::get_rbio($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: value corresponding to openssl's BIO structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_rbio.html>

       o   get_read_ahead

            my $rv = Net::SSLeay::get_read_ahead($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: (integer) read_ahead value

       o   set_read_ahead

            Net::SSLeay::set_read_ahead($ssl, $val);
            # $ssl - value corresponding to openssl's SSL structure
            # $val - read_ahead value to be set
            #
            # returns: the original read_ahead value

       o   get_server_random

           Returns internal SSLv3 server_random value.

            Net::SSLeay::get_server_random($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: server_random value (binary data)

       o   get_client_random

           NOTE: Does not exactly correspond to any low level API function

           Returns internal SSLv3 client_random value.

            Net::SSLeay::get_client_random($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: client_random value (binary data)

       o   export_keying_material

           Returns a buffer of $req_len bytes of keying material based on the
           constant string $label using the masterkey and client and server
           random strings as described in draft-ietf-pppext-eap-ttls-01.txt
           and See rfc2716 If p is present, it will be concatenated before
           generating the keying material Returns undef on error

               my $out = Net::SSLeay::export_keying_material($ssl, $req_len, $label, $p);

       o   get_session

           Retrieve TLS/SSL session data used in $ssl. The reference count of
           the SSL_SESSION is NOT incremented.

            my $rv = Net::SSLeay::get_session($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: value corresponding to openssl's SSL_SESSION structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_session.html>

       o   SSL_get0_session

           The alias for "get_session" (note that the name is
           "SSL_get0_session" NOT "get0_session").

            my $rv = Net::SSLeay::SSL_get0_session();

       o   get1_session

           Returns a pointer to the SSL_SESSION actually used in $ssl. The
           reference count of the SSL_SESSION is incremented by 1.

            my $rv = Net::SSLeay::get1_session($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: value corresponding to openssl's SSL_SESSION structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_session.html>

       o   get_shared_ciphers

           Returns string with a list (colon ':' separated) of ciphers shared
           between client and server within SSL session $ssl.

            my $rv = Net::SSLeay::get_shared_ciphers()
            #
            # returns: string like 'ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES256-SHA:DHE-DSS-AES256-SHA:...'

       o   get_shutdown

           Returns the shutdown mode of $ssl.

            my $rv = Net::SSLeay::get_shutdown($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: shutdown mode (bitmask) of ssl

            #to decode the return value (bitmask) use:
            0 - No shutdown setting, yet
            1 - SSL_SENT_SHUTDOWN
            2 - SSL_RECEIVED_SHUTDOWN

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_set_shutdown.html>

       o   get_ssl_method

           Returns a function pointer to the TLS/SSL method set in $ssl.

            my $rv = Net::SSLeay::get_ssl_method($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_ssl_version.html>

       o   get_state

           Returns the SSL connection state.

            my $rv = Net::SSLeay::get_state($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: (integer) state value
            #          to decode the returned state check:
            #          SSL_ST_* constants in openssl/ssl.h
            #          SSL2_ST_* constants in openssl/ssl2.h
            #          SSL23_ST_* constants in openssl/ssl23.h
            #          SSL3_ST_* + DTLS1_ST_* constants in openssl/ssl3.h

       o   state

           Exactly the same as "get_state".

            my $rv = Net::SSLeay::state($ssl);

       o   set_state

           Sets the SSL connection state.

            Net::SSLeay::set_state($ssl,Net::SSLeay::SSL_ST_ACCEPT());

           Not available with OpenSSL 1.1 and later.

       o   get_verify_depth

           Returns the verification depth limit currently set in $ssl.

            my $rv = Net::SSLeay::get_verify_depth($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: current depth or -1 if no limit has been explicitly set

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_get_verify_mode.html>

       o   set_verify_depth

           Sets the maximum depth for the certificate chain verification that
           shall be allowed for $ssl.

            Net::SSLeay::set_verify_depth($ssl, $depth);
            # $ssl - value corresponding to openssl's SSL structure
            # $depth - (integer) depth
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_verify.html>

       o   get_verify_mode

           Returns the verification mode (bitmask) currently set in $ssl.

            my $rv = Net::SSLeay::get_verify_mode($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: mode (bitmask)

           To decode the return value (bitmask) see documentation for
           "CTX_get_verify_mode".

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_get_verify_mode.html>

       o   set_verify

           Sets the verification flags for $ssl to be $mode and specifies the
           $verify_callback function to be used.

            Net::SSLeay::set_verify($ssl, $mode, $callback);
            # $ssl - value corresponding to openssl's SSL structure
            # $mode - mode (bitmask)
            # $callback - [optional] reference to perl callback function
            #
            # returns: no return value

           For $mode bitmask details see "CTX_get_verify_mode".

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_verify.html>

       o   get_verify_result

           Returns the result of the verification of the X509 certificate
           presented by the peer, if any.

            my $rv = Net::SSLeay::get_verify_result($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: (integer)
            #      0 - X509_V_OK: ok
            #      2 - X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT: unable to get issuer certificate
            #      3 - X509_V_ERR_UNABLE_TO_GET_CRL: unable to get certificate CRL
            #      4 - X509_V_ERR_UNABLE_TO_DECRYPT_CERT_SIGNATURE: unable to decrypt certificate's signature
            #      5 - X509_V_ERR_UNABLE_TO_DECRYPT_CRL_SIGNATURE: unable to decrypt CRL's signature
            #      6 - X509_V_ERR_UNABLE_TO_DECODE_ISSUER_PUBLIC_KEY: unable to decode issuer public key
            #      7 - X509_V_ERR_CERT_SIGNATURE_FAILURE: certificate signature failure
            #      8 - X509_V_ERR_CRL_SIGNATURE_FAILURE: CRL signature failure
            #      9 - X509_V_ERR_CERT_NOT_YET_VALID: certificate is not yet valid
            #     10 - X509_V_ERR_CERT_HAS_EXPIRED: certificate has expired
            #     11 - X509_V_ERR_CRL_NOT_YET_VALID: CRL is not yet valid
            #     12 - X509_V_ERR_CRL_HAS_EXPIRED: CRL has expired
            #     13 - X509_V_ERR_ERROR_IN_CERT_NOT_BEFORE_FIELD: format error in certificate's notBefore field
            #     14 - X509_V_ERR_ERROR_IN_CERT_NOT_AFTER_FIELD: format error in certificate's notAfter field
            #     15 - X509_V_ERR_ERROR_IN_CRL_LAST_UPDATE_FIELD: format error in CRL's lastUpdate field
            #     16 - X509_V_ERR_ERROR_IN_CRL_NEXT_UPDATE_FIELD: format error in CRL's nextUpdate field
            #     17 - X509_V_ERR_OUT_OF_MEM: out of memory
            #     18 - X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT: self signed certificate
            #     19 - X509_V_ERR_SELF_SIGNED_CERT_IN_CHAIN: self signed certificate in certificate chain
            #     20 - X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY: unable to get local issuer certificate
            #     21 - X509_V_ERR_UNABLE_TO_VERIFY_LEAF_SIGNATURE: unable to verify the first certificate
            #     22 - X509_V_ERR_CERT_CHAIN_TOO_LONG: certificate chain too long
            #     23 - X509_V_ERR_CERT_REVOKED: certificate revoked
            #     24 - X509_V_ERR_INVALID_CA: invalid CA certificate
            #     25 - X509_V_ERR_PATH_LENGTH_EXCEEDED: path length constraint exceeded
            #     26 - X509_V_ERR_INVALID_PURPOSE: unsupported certificate purpose
            #     27 - X509_V_ERR_CERT_UNTRUSTED: certificate not trusted
            #     28 - X509_V_ERR_CERT_REJECTED: certificate rejected
            #     29 - X509_V_ERR_SUBJECT_ISSUER_MISMATCH: subject issuer mismatch
            #     30 - X509_V_ERR_AKID_SKID_MISMATCH: authority and subject key identifier mismatch
            #     31 - X509_V_ERR_AKID_ISSUER_SERIAL_MISMATCH: authority and issuer serial number mismatch
            #     32 - X509_V_ERR_KEYUSAGE_NO_CERTSIGN:key usage does not include certificate signing
            #     50 - X509_V_ERR_APPLICATION_VERIFICATION: application verification failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_verify_result.html>

       o   set_verify_result

           Override result of peer certificate verification.

            Net::SSLeay::set_verify_result($ssl, $v);
            # $ssl - value corresponding to openssl's SSL structure
            # $v - (integer) result value
            #
            # returns: no return value

           For more info about valid return values see "get_verify_result"

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_set_verify_result.html>

       o   get_wbio

           Get 'write' BIO linked to an SSL object $ssl.

            my $rv = Net::SSLeay::get_wbio($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: value corresponding to openssl's BIO structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_get_rbio.html>

       o   load_client_CA_file

           Load X509 certificates from file (PEM formatted).

            my $rv = Net::SSLeay::load_client_CA_file($file);
            # $file - (string) file name
            #
            # returns: value corresponding to openssl's STACK_OF(X509_NAME) structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_load_client_CA_file.html>

       o   clear_num_renegotiations

           Executes SSL_CTRL_CLEAR_NUM_RENEGOTIATIONS command on $ssl.

            my $rv = Net::SSLeay::clear_num_renegotiations($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: command result

       o   need_tmp_RSA

           Executes SSL_CTRL_NEED_TMP_RSA command on $ssl.

            my $rv = Net::SSLeay::need_tmp_RSA($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: command result

           Not available with OpenSSL 1.1 and later.

       o   num_renegotiations

           Executes SSL_CTRL_GET_NUM_RENEGOTIATIONS command on $ssl.

            my $rv = Net::SSLeay::num_renegotiations($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: command result

       o   total_renegotiations

           Executes SSL_CTRL_GET_TOTAL_RENEGOTIATIONS command on $ssl.

            my $rv = Net::SSLeay::total_renegotiations($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: command result

       o   peek

           Copies $max bytes from the specified $ssl into the returned value.
           In contrast to the "Net::SSLeay::read()" function, the data in the
           SSL buffer is unmodified after the SSL_peek() operation.

            Net::SSLeay::peek($ssl, $max);
            # $ssl - value corresponding to openssl's SSL structure
            # $max - [optional] max bytes to peek (integer) - default is 32768
            #
            # in scalar context: data read from the TLS/SSL connection, undef on error
            # in list context:   two-item array consisting of data read (undef on error),
            #                      and return code from SSL_read().

       o   pending

           Obtain number of readable bytes buffered in $ssl object.

            my $rv = Net::SSLeay::pending($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: the number of bytes pending

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_pending.html>

       o   read

           Tries to read $max bytes from the specified $ssl.

            my $got = Net::SSLeay::read($ssl, $max);
            my($got, $rv) = Net::SSLeay::read($ssl, $max);
            # $ssl - value corresponding to openssl's SSL structure
            # $max - [optional] max bytes to read (integer) - default is 32768
            #
            # returns:
            # in scalar context: data read from the TLS/SSL connection, undef on error
            # in list context:   two-item array consisting of data read (undef on error),
            #                      and return code from SSL_read().

           Check openssl doc <http://www.openssl.org/docs/ssl/SSL_read.html>

       o   renegotiate

           Turn on flags for renegotiation so that renegotiation will happen

            my $rv = Net::SSLeay::renegotiate($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: 1 on success, 0 on failure

       o   rstate_string

           Returns a 2 letter string indicating the current read state of the
           SSL object $ssl.

            my $rv = Net::SSLeay::rstate_string($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: 2-letter string

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_rstate_string.html>

       o   rstate_string_long

           Returns a string indicating the current read state of the SSL
           object ssl.

            my $rv = Net::SSLeay::rstate_string_long($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: string with current state

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_rstate_string.html>

       o   session_reused

           Query whether a reused session was negotiated during handshake.

            my $rv = Net::SSLeay::session_reused($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: 0 - new session was negotiated; 1 - session was reused.

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_session_reused.html>

       o   set1_param

           Applies X509 verification parameters $vpm on $ssl

            my $rv = Net::SSLeay::set1_param($ssl, $vpm);
            # $ssl - value corresponding to openssl's SSL structure
            # $vpm - value corresponding to openssl's X509_VERIFY_PARAM structure
            #
            # returns: 1 on success, 0 on failure

       o   set_accept_state

           Sets $ssl to work in server mode.

            Net::SSLeay::set_accept_state($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_set_connect_state.html>

       o   set_bio

           Connects the BIOs $rbio and $wbio for the read and write operations
           of the TLS/SSL (encrypted) side of $ssl.

            Net::SSLeay::set_bio($ssl, $rbio, $wbio);
            # $ssl - value corresponding to openssl's SSL structure
            # $rbio - value corresponding to openssl's BIO structure
            # $wbio - value corresponding to openssl's BIO structure
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_set_bio.html>

       o   set_cipher_list

           Sets the list of ciphers only for ssl.

            my $rv = Net::SSLeay::set_cipher_list($ssl, $str);
            # $ssl - value corresponding to openssl's SSL structure
            # $str - (string) cipher list e.g. '3DES:+RSA'
            #
            # returns: 1 if any cipher could be selected and 0 on complete failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_cipher_list.html>

       o   set_client_CA_list

           Sets the list of CAs sent to the client when requesting a client
           certificate for the chosen $ssl, overriding the setting valid for
           $ssl's SSL_CTX object.

            my $rv = Net::SSLeay::set_client_CA_list($ssl, $list);
            # $ssl - value corresponding to openssl's SSL structure
            # $list - value corresponding to openssl's STACK_OF(X509_NAME) structure
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_client_CA_list.html>

       o   set_connect_state

           Sets $ssl to work in client mode.

            Net::SSLeay::set_connect_state($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_set_connect_state.html>

       o   set_fd

           Sets the file descriptor $fd as the input/output facility for the
           TLS/SSL (encrypted) side of $ssl, $fd will typically be the socket
           file descriptor of a network connection.

            my $rv = Net::SSLeay::set_fd($ssl, $fd);
            # $ssl - value corresponding to openssl's SSL structure
            # $fd - (integer) file handle (got via perl's fileno)
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc <http://www.openssl.org/docs/ssl/SSL_set_fd.html>

       o   set_psk_client_callback

           Sets the psk client callback.

            Net::SSLeay::set_psk_client_callback($ssl, sub { my $hint = shift; return ($identity, $key) } );
            # $ssl - value corresponding to openssl's SSL structure
            # $hint - PSK identity hint send by the server
            # $identity - PSK identity
            # $key - PSK key, hex string without the leading '0x', e.g. 'deadbeef'
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_set_psk_client_callback.html>

       o   set_rfd

           Sets the file descriptor $fd as the input (read) facility for the
           TLS/SSL (encrypted) side of $ssl.

            my $rv = Net::SSLeay::set_rfd($ssl, $fd);
            # $ssl - value corresponding to openssl's SSL structure
            # $fd - (integer) file handle (got via perl's fileno)
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc <http://www.openssl.org/docs/ssl/SSL_set_fd.html>

       o   set_wfd

            my $rv = Net::SSLeay::set_wfd($ssl, $fd);
            # $ssl - value corresponding to openssl's SSL structure
            # $fd - (integer) file handle (got via perl's fileno)
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc <http://www.openssl.org/docs/ssl/SSL_set_fd.html>

       o   set_info_callback

           Sets the callback function, that can be used to obtain state
           information for $ssl during connection setup and use.  When
           callback is undef, the callback setting currently valid for ctx is
           used.

            Net::SSLeay::set_info_callback($ssl, $cb, [$data]);
            # $ssl - value corresponding to openssl's SSL structure
            # $cb - sub { my ($ssl,$where,$ret,$data) = @_; ... }
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_info_callback.html>

       o   CTX_set_info_callback

           Sets the callback function on ctx, that can be used to obtain state
           information during ssl connection setup and use.  When callback is
           undef, an existing callback will be disabled.

            Net::SSLeay::CTX_set_info_callback($ssl, $cb, [$data]);
            # $ssl - value corresponding to openssl's SSL structure
            # $cb - sub { my ($ssl,$where,$ret,$data) = @_; ... }
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_info_callback.html>

       o   set_pref_cipher

           Sets the list of available ciphers for $ssl using the control
           string $str.

            my $rv = Net::SSLeay::set_pref_cipher($ssl, $str);
            # $ssl - value corresponding to openssl's SSL structure
            # $str - (string) cipher list e.g. '3DES:+RSA'
            #
            # returns: 1 if any cipher could be selected and 0 on complete failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_cipher_list.html>

       o   CTX_set_psk_client_callback

           Sets the psk client callback.

            Net::SSLeay::CTX_set_psk_client_callback($ssl, sub { my $hint = shift; return ($identity, $key) } );
            # $ssl - value corresponding to openssl's SSL structure
            # $hint - PSK identity hint send by the server
            # $identity - PSK identity
            # $key - PSK key, hex string without the leading '0x', e.g. 'deadbeef'
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_psk_client_callback.html>

       o   set_purpose

            my $rv = Net::SSLeay::set_purpose($ssl, $purpose);
            # $ssl - value corresponding to openssl's SSL structure
            # $purpose - (integer) purpose identifier
            #
            # returns: 1 on success, 0 on failure

           For more info about available $purpose identifiers see
           "CTX_set_purpose".

       o   set_quiet_shutdown

           Sets the 'quiet shutdown' flag for $ssl to be $mode.

            Net::SSLeay::set_quiet_shutdown($ssl, $mode);
            # $ssl - value corresponding to openssl's SSL structure
            # $mode - 0 or 1
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_quiet_shutdown.html>

       o   set_session

           Set a TLS/SSL session to be used during TLS/SSL connect.

            my $rv = Net::SSLeay::set_session($to, $ses);
            # $to - value corresponding to openssl's SSL structure
            # $ses - value corresponding to openssl's SSL_SESSION structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_set_session.html>

       o   set_session_id_context

           Sets the context $sid_ctx of length $sid_ctx_len within which a
           session can be reused for the $ssl object.

            my $rv = Net::SSLeay::set_session_id_context($ssl, $sid_ctx, $sid_ctx_len);
            # $ssl - value corresponding to openssl's SSL structure
            # $sid_ctx - data buffer
            # $sid_ctx_len - length of data in $sid_ctx
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_session_id_context.html>

       o   set_session_secret_cb

           Setup pre-shared secret session resumption function.

            Net::SSLeay::set_session_secret_cb($ssl, $func, $data);
            # $ssl - value corresponding to openssl's SSL structure
            # $func - perl reference to callback function
            # $data - [optional] data that will be passed to callback function when invoked
            #
            # returns: no return value

           The callback function will be called like:
           callback_function($secret, $ciphers, $pref_cipher, $data);

           # $secret is the current master session key, usually all 0s at the
           beginning of a session # $ciphers is ref to an array of peer cipher
           names # $pref_cipher is a ref to an index into the list of cipher
           names of #  the preferred cipher. Set it if you want to specify a
           preferred cipher # $data is the data passed to
           set_session_secret_cb

           The callback function should return 1 if it likes the suggested
           cipher (or has selected an alternative by setting pref_cipher),
           else it should return 0 (in which case OpenSSL will select its own
           preferred cipher).

           With OpenSSL 1.1 and later, callback_function can change the master
           key for the session by altering $secret and returning 1.

       o   CTX_set_tlsext_ticket_getkey_cb

           Setup encryption for TLS session tickets (stateless session reuse).

            Net::SSLeay::CTX_set_tlsext_ticket_getkey_cb($ctx, $func, $data);
            # $ctx  - value corresponding to openssl's SSL_CTX structure
            # $func - perl reference to callback function
            # $data - [optional] data that will be passed to callback function when invoked
            #
            # returns: no return value

           The callback function will be called like:
           getkey($data,[$key_name]) -> ($key,$current_key_name)

           # $data is the data passed to set_session_secret_cb # $key_name is
           the name of the key OpenSSL has extracted from the session ticket #
           $key is the requested key for ticket encryption + HMAC #
           $current_key_name is the name for the currently valid key

           OpenSSL will call the function without a key name if it generates a
           new ticket.  It then needs the callback to return the
           encryption+HMAC key and an identifier (key name) for this key.

           When OpenSSL gets a session ticket from the client it extracts the
           key name and calls the callback with this name as argument. It then
           expects the callback to return the encryption+HMAC key matching the
           requested key name and and also the key name which should be used
           at the moment. If the requested key name and the returned key name
           differ it means that this session ticket was created with an
           expired key and need to be renewed. In this case OpenSSL will call
           the callback again with no key name to create a new session ticket
           based on the old one.

           The key must be at least 32 byte of random data which can be
           created with RAND_bytes. Internally the first 16 byte are used as
           key in AES-128 encryption while the next 16 byte are used for the
           SHA-256 HMAC.  The key name are binary data and must be exactly 16
           byte long.

           Example:

               Net::SSLeay::RAND_bytes(my $oldkey,32);
               Net::SSLeay::RAND_bytes(my $newkey,32);
               my $oldkey_name = pack("a16",'oldsecret');
               my $newkey_name = pack("a16",'newsecret');

               my @keys = (
                   [ $newkey_name, $newkey ], # current active key
                   [ $oldkey_name, $oldkey ], # already expired
               );

               Net::SSLeay::CTX_set_tlsext_ticket_getkey_cb($server2->_ctx, sub {
                   my ($mykeys,$name) = @_;

                   # return (current_key, current_key_name) if no name given
                   return ($mykeys->[0][1],$mykeys->[0][0]) if ! $name;

                   # return (matching_key, current_key_name) if we find a key matching
                   # the given name
                   for(my $i = 0; $i<@$mykeys; $i++) {
                       next if $name ne $mykeys->[$i][0];
                       return ($mykeys->[$i][1],$mykeys->[0][0]);
                   }

                   # no matching key found
                   return;
               },\@keys);

           This function is based on the OpenSSL function
           SSL_CTX_set_tlsext_ticket_key_cb but provides a simpler to use
           interface. For more information see
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_tlsext_ticket_key_cb.html>

       o   set_session_ticket_ext_cb

           Setup callback for TLS session tickets (stateless session reuse).

            Net::SSLeay::set_session_ticket_ext_cb($ssl, $func, $data);
            # $ssl  - value corresponding to openssl's SSL structure
            # $func - perl reference to callback function
            # $data - [optional] data that will be passed to callback function when invoked
            #
            # returns: no return value

           The callback function will be called like:
           getticket($ssl,$ticket,$data) -> $return_value

           # $ssl is a value corresponding to openssl's SSL structure #
           $ticket is a value of received TLS session ticket (can also be
           empty) # $data is the data passed to set_session_ticket_ext_cb #
           $return_value is either 0 (failure) or 1 (success)

           This function is based on the OpenSSL function
           SSL_set_session_ticket_ext_cb.

       o   set_session_ticket_ext

           Set TLS session ticket (stateless session reuse).

            Net::SSLeay::set_session_ticket_ext($ssl, $ticket);
            # $ssl    - value corresponding to openssl's SSL structure
            # $ticket - is a value of TLS session ticket which client will send (can also be empty string)
            #
            # returns: no return value

           The callback function will be called like:
           getticket($ssl,$ticket,$data) -> $return_value

           # $ssl is a value corresponding to openssl's SSL structure #
           $ticket is a value of received TLS session ticket (can also be
           empty) # $data is the data passed to set_session_ticket_ext_cb #
           $return_value is either 0 (failure) or 1 (success)

           This function is based on the OpenSSL function
           SSL_set_session_ticket_ext_cb.

       o   set_shutdown

           Sets the shutdown state of $ssl to $mode.

            Net::SSLeay::set_shutdown($ssl, $mode);
            # $ssl - value corresponding to openssl's SSL structure
            # $mode - (integer) shutdown mode:
            #         0 - No shutdown
            #         1 - SSL_SENT_SHUTDOWN
            #         2 - SSL_RECEIVED_SHUTDOWN
            #         3 - SSL_RECEIVED_SHUTDOWN+SSL_SENT_SHUTDOWN
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_set_shutdown.html>

       o   set_ssl_method

           Sets a new TLS/SSL method for a particular $ssl object.

            my $rv = Net::SSLeay::set_ssl_method($ssl, $method);
            # $ssl - value corresponding to openssl's SSL structure
            # $method - value corresponding to openssl's SSL_METHOD structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_ssl_version.html>

       o   set_tmp_dh

           Sets DH parameters to be used to be $dh.

            my $rv = Net::SSLeay::set_tmp_dh($ssl, $dh);
            # $ssl - value corresponding to openssl's SSL structure
            # $dh - value corresponding to openssl's DH structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_dh_callback.html>

       o   set_tmp_dh_callback

           Sets the callback function for $ssl to be used when a DH parameters
           are required to $dh_cb.

           ??? (does this function really work?)

            Net::SSLeay::set_tmp_dh_callback($ssl, $dh);
            # $ssl - value corresponding to openssl's SSL structure
            # $dh_cb - pointer to function ???
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_dh_callback.html>

       o   set_tmp_rsa

           Sets the temporary/ephemeral RSA key to be used in $ssl to be $rsa.

            my $rv = Net::SSLeay::set_tmp_rsa($ssl, $rsa);
            # $ssl - value corresponding to openssl's SSL structure
            # $rsa - value corresponding to openssl's RSA structure
            #
            # returns: 1 on success, 0 on failure

           Example:

            $rsakey = Net::SSLeay::RSA_generate_key();
            Net::SSLeay::set_tmp_rsa($ssl, $rsakey);
            Net::SSLeay::RSA_free($rsakey);

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_rsa_callback.html>

       o   set_tmp_rsa_callback

           Sets the callback function for $ssl to be used when a
           temporary/ephemeral RSA key is required to $tmp_rsa_callback.

           ??? (does this function really work?)

            Net::SSLeay::set_tmp_rsa_callback($ssl, $tmp_rsa_callback);
            # $ssl - value corresponding to openssl's SSL structure
            # $tmp_rsa_callback - (function pointer) ???
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_rsa_callback.html>

       o   set_trust

            my $rv = Net::SSLeay::set_trust($ssl, $trust);
            # $ssl - value corresponding to openssl's SSL structure
            # $trust - (integer) trust identifier
            #
            # returns: the original value

           For more details about $trust values see "CTX_set_trust".

       o   shutdown

           Shuts down an active TLS/SSL connection. It sends the 'close
           notify' shutdown alert to the peer.

            my $rv = Net::SSLeay::shutdown($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: 1 - shutdown was successfully completed
            #          0 - shutdown is not yet finished,
            #         -1 - shutdown was not successful

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_shutdown.html>

       o   state_string

           Returns a 6 letter string indicating the current state of the SSL
           object $ssl.

            my $rv = Net::SSLeay::state_string($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: 6-letter string

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_state_string.html>

       o   state_string_long

           Returns a string indicating the current state of the SSL object
           $ssl.

            my $rv = Net::SSLeay::state_string_long($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: state strings

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_state_string.html>

       o   use_PrivateKey

           Adds $pkey as private key to $ssl.

            my $rv = Net::SSLeay::use_PrivateKey($ssl, $pkey);
            # $ssl - value corresponding to openssl's SSL structure
            # $pkey - value corresponding to openssl's EVP_PKEY structure
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   use_PrivateKey_ASN1

           Adds the private key of type $pk stored in $data to $ssl.

            my $rv = Net::SSLeay::use_PrivateKey_ASN1($pk, $ssl, $d, $len);
            # $pk - (integer) key type, NID of corresponding algorithm
            # $ssl - value corresponding to openssl's SSL structure
            # $data - key data (binary)
            # $len - length of $data
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   use_PrivateKey_file

           Adds the first private key found in $file to $ssl.

            my $rv = Net::SSLeay::use_PrivateKey_file($ssl, $file, $type);
            # $ssl - value corresponding to openssl's SSL structure
            # $file - (string) file name
            # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   use_RSAPrivateKey

           Adds $rsa as RSA private key to $ssl.

            my $rv = Net::SSLeay::use_RSAPrivateKey($ssl, $rsa);
            # $ssl - value corresponding to openssl's SSL structure
            # $rsa - value corresponding to openssl's RSA structure
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   use_RSAPrivateKey_ASN1

           Adds RSA private key stored in $data to $ssl.

            my $rv = Net::SSLeay::use_RSAPrivateKey_ASN1($ssl, $data, $len);
            # $ssl - value corresponding to openssl's SSL structure
            # $data - key data (binary)
            # $len - length of $data
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   use_RSAPrivateKey_file

           Adds the first RSA private key found in $file to $ssl.

            my $rv = Net::SSLeay::use_RSAPrivateKey_file($ssl, $file, $type);
            # $ssl - value corresponding to openssl's SSL structure
            # $file - (string) file name
            # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   use_certificate

           Loads the certificate $x into $ssl.

            my $rv = Net::SSLeay::use_certificate($ssl, $x);
            # $ssl - value corresponding to openssl's SSL structure
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   use_certificate_ASN1

           Loads the ASN1 encoded certificate from $data to $ssl.

            my $rv = Net::SSLeay::use_certificate_ASN1($ssl, $data, $len);
            # $ssl - value corresponding to openssl's SSL structure
            # $data - certificate data (binary)
            # $len - length of $data
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   use_certificate_file

           Loads the first certificate stored in $file into $ssl.

            my $rv = Net::SSLeay::use_certificate_file($ssl, $file, $type);
            # $ssl - value corresponding to openssl's SSL structure
            # $file - (string) file name
            # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
            #
            # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

       o   version

           Returns SSL/TLS protocol version

            my $rv = Net::SSLeay::version($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: (integer) protocol version
            #          0x0002 - SSL2_VERSION  (SSLv2)
            #          0x0300 - SSL3_VERSION  (SSLv3)
            #          0x0301 - TLS1_VERSION  (TLSv1)
            #          0xFEFF - DTLS1_VERSION (DTLSv1)

       o   want

           Returns state information for the SSL object $ssl.

            my $rv = Net::SSLeay::want($ssl);
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: state
            #          1 - SSL_NOTHING
            #          2 - SSL_WRITING
            #          3 - SSL_READING
            #          4 - SSL_X509_LOOKUP

           Check openssl doc <http://www.openssl.org/docs/ssl/SSL_want.html>

       o   write

           Writes data from the buffer $data into the specified $ssl
           connection.

            my $rv = Net::SSLeay::write($ssl, $data);
            # $ssl - value corresponding to openssl's SSL structure
            # $data - data to be written
            #
            # returns: >0 - (success) number of bytes actually written to the TLS/SSL connection
            #           0 - write not successful, probably the underlying connection was closed
            #          <0 - error

           Check openssl doc <http://www.openssl.org/docs/ssl/SSL_write.html>

       o   write_partial

           NOTE: Does not exactly correspond to any low level API function

           Writes a fragment of data in $data from the buffer $data into the
           specified $ssl connection.

            my $rv = Net::SSLeay::write_partial($ssl, $from, $count, $data);
            # $ssl - value corresponding to openssl's SSL structure
            # $from - (integer) offset from the beginning of $data
            # $count - (integer) length of data to be written
            # $data - data buffer
            #
            # returns: >0 - (success) number of bytes actually written to the TLS/SSL connection
            #           0 - write not successful, probably the underlying connection was closed
            #          <0 - error

       o   set_tlsext_host_name

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.8f

           Sets TLS servername extension on SLL object $ssl to value $name.

            my $rv = set_tlsext_host_name($ssl, $name);
            # $ssl - value corresponding to openssl's SSL structure
            # $name - (string) name to be set
            #
            # returns: 1 on success, 0 on failure

       Low level API: RAND_* related functions

       Check openssl doc related to RAND stuff
       <http://www.openssl.org/docs/crypto/rand.html>

       o   RAND_add

           Mixes the $num bytes at $buf into the PRNG state.

            Net::SSLeay::RAND_add($buf, $num, $entropy);
            # $buf - buffer with data to be mixed into the PRNG state
            # $num - number of bytes in $buf
            # $entropy - estimate of how much randomness is contained in $buf (in bytes)
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/RAND_add.html>

       o   RAND_seed

           Equivalent to "RAND_add" when $num == $entropy.

            Net::SSLeay::RAND_seed($buf);   # Perlishly figures out buf size
            # $buf - buffer with data to be mixed into the PRNG state
            # $num - number of bytes in $buf
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/RAND_add.html>

       o   RAND_status

           Gives PRNG status (seeded enough or not).

            my $rv = Net::SSLeay::RAND_status();
            #returns: 1 if the PRNG has been seeded with enough data, 0 otherwise

           Check openssl doc
           <http://www.openssl.org/docs/crypto/RAND_add.html>

       o   RAND_bytes

           Puts $num cryptographically strong pseudo-random bytes into $buf.

            my $rv = Net::SSLeay::RAND_bytes($buf, $num);
            # $buf - buffer where the random data will be stored
            # $num - the size (in bytes) of requested random data
            #
            # returns: 1 on success, 0 otherwise

           Check openssl doc
           <http://www.openssl.org/docs/crypto/RAND_bytes.html>

       o   RAND_pseudo_bytes

           Puts $num pseudo-random (not necessarily unpredictable) bytes into
           $buf.

            my $rv = Net::SSLeay::RAND_pseudo_bytes($buf, $num);
            # $buf - buffer where the random data will be stored
            # $num - the size (in bytes) of requested random data
            #
            # returns: 1 if the bytes generated are cryptographically strong, 0 otherwise

           Check openssl doc
           <http://www.openssl.org/docs/crypto/RAND_bytes.html>

       o   RAND_cleanup

           Erase the PRNG state.

            Net::SSLeay::RAND_cleanup();
            # no args, no return value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/RAND_cleanup.html>

       o   RAND_egd_bytes

           Queries the entropy gathering daemon EGD on socket $path for $bytes
           bytes.

            my $rv = Net::SSLeay::RAND_egd_bytes($path, $bytes);
            # $path - path to a socket of entropy gathering daemon EGD
            # $bytes - number of bytes we want from EGD
            #
            # returns: the number of bytes read from the daemon on success, and -1 on failure

           Check openssl doc
           <http://www.openssl.org/docs/crypto/RAND_egd.html>

       o   RAND_file_name

           Generates a default path for the random seed file.

            my $file = Net::SSLeay::RAND_file_name($num);
            # $num - maximum size of returned file name
            #
            # returns: string with file name on success, '' (empty string) on failure

           Check openssl doc
           <http://www.openssl.org/docs/crypto/RAND_load_file.html>

       o   RAND_load_file

           Reads $max_bytes of bytes from $file_name and adds them to the
           PRNG.

            my $rv = Net::SSLeay::RAND_load_file($file_name, $max_bytes);
            # $file_name - the name of file
            # $max_bytes - bytes to read from $file_name; -1 => the complete file is read
            #
            # returns: the number of bytes read

           Check openssl doc
           <http://www.openssl.org/docs/crypto/RAND_load_file.html>

       o   RAND_write_file

           Writes 1024 random bytes to $file_name which can be used to
           initialize the PRNG by calling "RAND_load_file" in a later session.

            my $rv = Net::SSLeay::RAND_write_file($file_name);
            # $file_name - the name of file
            #
            # returns: the number of bytes written, and -1 if the bytes written were generated without appropriate seed

           Check openssl doc
           <http://www.openssl.org/docs/crypto/RAND_load_file.html>

       o   RAND_poll

           Collects some entropy from operating system and adds it to the
           PRNG.

            my $rv = Net::SSLeay::RAND_poll();
            # returns: 1 on success, 0 on failure (unable to gather reasonable entropy)

       Low level API: OBJ_* related functions

       o   OBJ_cmp

           Compares ASN1_OBJECT $a to ASN1_OBJECT $b.

            my $rv = Net::SSLeay::OBJ_cmp($a, $b);
            # $a - value corresponding to openssl's ASN1_OBJECT structure
            # $b - value corresponding to openssl's ASN1_OBJECT structure
            #
            # returns: if the two are identical 0 is returned

           Check openssl doc
           <http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

       o   OBJ_dup

           Returns a copy/duplicate of $o.

            my $rv = Net::SSLeay::OBJ_dup($o);
            # $o - value corresponding to openssl's ASN1_OBJECT structure
            #
            # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

       o   OBJ_nid2ln

           Returns long name for given NID $n.

            my $rv = Net::SSLeay::OBJ_nid2ln($n);
            # $n - (integer) NID
            #
            # returns: (string) long name e.g. 'commonName'

           Check openssl doc
           <http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

       o   OBJ_ln2nid

           Returns NID corresponding to given long name $n.

            my $rv = Net::SSLeay::OBJ_ln2nid($s);
            # $s - (string) long name e.g. 'commonName'
            #
            # returns: (integer) NID

       o   OBJ_nid2sn

           Returns short name for given NID $n.

            my $rv = Net::SSLeay::OBJ_nid2sn($n);
            # $n - (integer) NID
            #
            # returns: (string) short name e.g. 'CN'

           Example:

            print Net::SSLeay::OBJ_nid2sn(&Net::SSLeay::NID_commonName);

       o   OBJ_sn2nid

           Returns NID corresponding to given short name $s.

            my $rv = Net::SSLeay::OBJ_sn2nid($s);
            # $s - (string) short name e.g. 'CN'
            #
            # returns: (integer) NID

           Example:

            print "NID_commonName constant=", &Net::SSLeay::NID_commonName;
            print "OBJ_sn2nid('CN')=", Net::SSLeay::OBJ_sn2nid('CN');

       o   OBJ_nid2obj

           Returns ASN1_OBJECT for given NID $n.

            my $rv = Net::SSLeay::OBJ_nid2obj($n);
            # $n - (integer) NID
            #
            # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

       o   OBJ_obj2nid

           Returns NID corresponding to given ASN1_OBJECT $o.

            my $rv = Net::SSLeay::OBJ_obj2nid($o);
            # $o - value corresponding to openssl's ASN1_OBJECT structure
            #
            # returns: (integer) NID

           Check openssl doc
           <http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

       o   OBJ_txt2obj

           Converts the text string s into an ASN1_OBJECT structure. If
           $no_name is 0 then long names (e.g. 'commonName') and short names
           (e.g. 'CN') will be interpreted as well as numerical forms (e.g.
           '2.5.4.3'). If $no_name is 1 only the numerical form is acceptable.

            my $rv = Net::SSLeay::OBJ_txt2obj($s, $no_name);
            # $s - text string to be converted
            # $no_name - (integer) 0 or 1
            #
            # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

       o   OBJ_obj2txt

           Converts the ASN1_OBJECT a into a textual representation.

            Net::SSLeay::OBJ_obj2txt($a, $no_name);
            # $a - value corresponding to openssl's ASN1_OBJECT structure
            # $no_name - (integer) 0 or 1
            #
            # returns: textual representation e.g. 'commonName' ($no_name=0), '2.5.4.3' ($no_name=1)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

       o   OBJ_txt2nid

           Returns NID corresponding to text string $s which can be a long
           name, a short name or the numerical representation of an object.

            my $rv = Net::SSLeay::OBJ_txt2nid($s);
            # $s - (string) e.g. 'commonName' or 'CN' or '2.5.4.3'
            #
            # returns: (integer) NID

           Example:

            my $nid = Net::SSLeay::OBJ_txt2nid('2.5.4.3');
            Net::SSLeay::OBJ_nid2sn($n);

           Check openssl doc
           <http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

       Low level API: ASN1_INTEGER_* related functions

       o   ASN1_INTEGER_new

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Creates a new ASN1_INTEGER structure.

            my $rv = Net::SSLeay::ASN1_INTEGER_new();
            #
            # returns: value corresponding to openssl's ASN1_INTEGER structure (0 on failure)

       o   ASN1_INTEGER_free

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Free an allocated ASN1_INTEGER structure.

            Net::SSLeay::ASN1_INTEGER_free($i);
            # $i - value corresponding to openssl's ASN1_INTEGER structure
            #
            # returns: no return value

       o   ASN1_INTEGER_get

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns integer value of given ASN1_INTEGER object.

           BEWARE: If the value stored in ASN1_INTEGER is greater than max.
           integer that can be stored in 'long' type (usually 32bit but may
           vary according to platform) then this function will return -1.  For
           getting large ASN1_INTEGER values consider using
           "P_ASN1_INTEGER_get_dec" or "P_ASN1_INTEGER_get_hex".

            my $rv = Net::SSLeay::ASN1_INTEGER_get($a);
            # $a - value corresponding to openssl's ASN1_INTEGER structure
            #
            # returns: integer value of ASN1_INTEGER object in $a

       o   ASN1_INTEGER_set

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets value of given ASN1_INTEGER object to value $val

           BEWARE: $val has max. limit (= max. integer that can be stored in
           'long' type).  For setting large ASN1_INTEGER values consider using
           "P_ASN1_INTEGER_set_dec" or "P_ASN1_INTEGER_set_hex".

            my $rv = Net::SSLeay::ASN1_INTEGER_set($i, $val);
            # $i - value corresponding to openssl's ASN1_INTEGER structure
            # $val - integer value
            #
            # returns: 1 on success, 0 on failure

       o   P_ASN1_INTEGER_get_dec

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns string with decimal representation of integer value of
           given ASN1_INTEGER object.

            Net::SSLeay::P_ASN1_INTEGER_get_dec($i);
            # $i - value corresponding to openssl's ASN1_INTEGER structure
            #
            # returns: string with decimal representation

       o   P_ASN1_INTEGER_get_hex

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns string with hexadecimal representation of integer value of
           given ASN1_INTEGER object.

            Net::SSLeay::P_ASN1_INTEGER_get_hex($i);
            # $i - value corresponding to openssl's ASN1_INTEGER structure
            #
            # returns: string with hexadecimal representation

       o   P_ASN1_INTEGER_set_dec

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets value of given ASN1_INTEGER object to value $val (decimal
           string, suitable for large integers)

            Net::SSLeay::P_ASN1_INTEGER_set_dec($i, $str);
            # $i - value corresponding to openssl's ASN1_INTEGER structure
            # $str - string with decimal representation
            #
            # returns: 1 on success, 0 on failure

       o   P_ASN1_INTEGER_set_hex

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets value of given ASN1_INTEGER object to value $val (hexadecimal
           string, suitable for large integers)

            Net::SSLeay::P_ASN1_INTEGER_set_hex($i, $str);
            # $i - value corresponding to openssl's ASN1_INTEGER structure
            # $str - string with hexadecimal representation
            #
            # returns: 1 on success, 0 on failure

       Low level API: ASN1_STRING_* related functions

       o   P_ASN1_STRING_get

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns string value of given ASN1_STRING object.

            Net::SSLeay::P_ASN1_STRING_get($s, $utf8_decode);
            # $s - value corresponding to openssl's ASN1_STRING structure
            # $utf8_decode - [optional] 0 or 1 whether the returned value should be utf8 decoded (default=0)
            #
            # returns: string

            $string = Net::SSLeay::P_ASN1_STRING_get($s);
            #is the same as:
            $string = Net::SSLeay::P_ASN1_STRING_get($s, 0);

       Low level API: ASN1_TIME_* related functions

       o   ASN1_TIME_new

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

            my $time = ASN1_TIME_new();
            # returns: value corresponding to openssl's ASN1_TIME structure

       o   ASN1_TIME_free

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

            ASN1_TIME_free($time);
            # $time - value corresponding to openssl's ASN1_TIME structure

       o   ASN1_TIME_set

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

            ASN1_TIME_set($time, $t);
            # $time - value corresponding to openssl's ASN1_TIME structure
            # $t - time value in seconds since 1.1.1970

           BEWARE: It is platform dependent how this function will handle
           dates after 2038.  Although perl's integer is large enough the
           internal implementation of this function is dependent on the size
           of time_t structure (32bit time_t has problem with 2038).

           If you want to safely set date and time after 2038 use function
           "P_ASN1_TIME_set_isotime".

       o   P_ASN1_TIME_get_isotime

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before;
           requires at least openssl-0.9.7e

           NOTE: Does not exactly correspond to any low level API function

           Gives ISO-8601 string representation of ASN1_TIME structure.

            my $datetime_string = P_ASN1_TIME_get_isotime($time);
            # $time - value corresponding to openssl's ASN1_TIME structure
            #
            # returns: datetime string like '2033-05-16T20:39:37Z' or '' on failure

           The output format is compatible with module
           DateTime::Format::RFC3339

       o   P_ASN1_TIME_set_isotime

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before;
           requires at least openssl-0.9.7e

           NOTE: Does not exactly correspond to any low level API function

           Sets time and date value of ANS1_time structure.

            my $rv = P_ASN1_TIME_set_isotime($time, $string);
            # $time - value corresponding to openssl's ASN1_TIME structure
            # $string - ISO-8601 timedate string like '2033-05-16T20:39:37Z'
            #
            # returns: 1 on success, 0 on failure

           The $string parameter has to be in full form like
           "2012-03-22T23:55:33" or "2012-03-22T23:55:33Z" or
           "2012-03-22T23:55:33CET". Short forms like "2012-03-22T23:55" or
           "2012-03-22" are not supported.

       o   P_ASN1_TIME_put2string

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before, has
           bugs with openssl-0.9.8i

           NOTE: Does not exactly correspond to any low level API function

           Gives string representation of ASN1_TIME structure.

            my $str = P_ASN1_TIME_put2string($time);
            # $time - value corresponding to openssl's ASN1_TIME structure
            #
            # returns: datetime string like 'May 16 20:39:37 2033 GMT'

       o   P_ASN1_UTCTIME_put2string

           NOTE: deprecated function, only for backward compatibility, just an
           alias for "P_ASN1_TIME_put2string"

       Low level API: X509_* related functions

       o   X509_new

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Allocates and initializes a X509 structure.

            my $rv = Net::SSLeay::X509_new();
            #
            # returns: value corresponding to openssl's X509 structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_new.html>

       o   X509_free

           Frees up the X509 structure.

            Net::SSLeay::X509_free($a);
            # $a - value corresponding to openssl's X509 structure
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_new.html>

       o   X509_check_host

           COMPATIBILITY: not available in Net-SSLeay-1.68 and before;
           requires at least OpenSSL 1.0.2.

           Checks f the certificate Subject Alternative Name (SAN) or Subject
           CommonName (CN) matches the specified host name.

            my $rv = Net::SSLeay::X509_check_host($cert, $name, $flags, $peername);
            # $cert - value corresponding to openssl's X509 structure
            # $name - host name to check
            # $flags (optional, default: 0) - can be the bitwise OR of:
            #   &Net::SSLeay::X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT
            #   &Net::SSLeay::X509_CHECK_FLAG_NO_WILDCARDS
            #   &Net::SSLeay::X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS
            #   &Net::SSLeay::X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS
            #   &Net::SSLeay::X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS
            # $peername (optional) - If not omitted and $host matches $cert,
            #                        a copy of the matching SAN or CN from
            #                        the peer certificate is stored in $peername.
            #
            # returns:
            #   1 for a successful match
            #   0 for a failed match
            #  -1 for an internal error
            #  -2 if the input is malformed

           Check openssl doc
           <https://www.openssl.org/docs/crypto/X509_check_host.html>.

       o   X509_check_email

           COMPATIBILITY: not available in Net-SSLeay-1.68 and before;
           requires at least OpenSSL 1.0.2.

           Checks if the certificate matches the specified email address.

            my $rv = Net::SSLeay::X509_check_email($cert, $address, $flags);
            # $cert - value corresponding to openssl's X509 structure
            # $address - email address to check
            # $flags (optional, default: 0) - see X509_check_host()
            #
            # returns: see X509_check_host()

           Check openssl doc
           <https://www.openssl.org/docs/crypto/X509_check_email.html>.

       o   X509_check_ip

           COMPATIBILITY: not available in Net-SSLeay-1.68 and before;
           requires at least OpenSSL 1.0.2.

           Checks if the certificate matches the specified IPv4 or IPv6
           address.

            my $rv = Net::SSLeay::X509_check_email($cert, $address, $flags);
            # $cert - value corresponding to openssl's X509 structure
            # $address - IP address to check in binary format, in network byte order
            # $flags (optional, default: 0) - see X509_check_host()
            #
            # returns: see X509_check_host()

           Check openssl doc
           <https://www.openssl.org/docs/crypto/X509_check_ip.html>.

       o   X509_check_ip_asc

           COMPATIBILITY: not available in Net-SSLeay-1.68 and before;
           requires at least OpenSSL 1.0.2.

           Checks if the certificate matches the specified IPv4 or IPv6
           address.

            my $rv = Net::SSLeay::X509_check_email($cert, $address, $flags);
            # $cert - value corresponding to openssl's X509 structure
            # $address - IP address to check in text representation
            # $flags (optional, default: 0) - see X509_check_host()
            #
            # returns: see X509_check_host()

           Check openssl doc
           <https://www.openssl.org/docs/crypto/X509_check_ip_asc.html>.

       o   X509_certificate_type

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns bitmask with type of certificate $x.

            my $rv = Net::SSLeay::X509_certificate_type($x);
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: (integer) bitmask with certificate type

            #to decode bitmask returned by this function use these constants:
            &Net::SSLeay::EVP_PKS_DSA
            &Net::SSLeay::EVP_PKS_EC
            &Net::SSLeay::EVP_PKS_RSA
            &Net::SSLeay::EVP_PKT_ENC
            &Net::SSLeay::EVP_PKT_EXCH
            &Net::SSLeay::EVP_PKT_EXP
            &Net::SSLeay::EVP_PKT_SIGN
            &Net::SSLeay::EVP_PK_DH
            &Net::SSLeay::EVP_PK_DSA
            &Net::SSLeay::EVP_PK_EC
            &Net::SSLeay::EVP_PK_RSA

       o   X509_digest

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Computes digest/fingerprint of X509 $data using $type hash
           function.

            my $digest_value = Net::SSLeay::X509_digest($data, $type);
            # $data - value corresponding to openssl's X509 structure
            # $type - value corresponding to openssl's EVP_MD structure - e.g. got via EVP_get_digestbyname()
            #
            # returns: hash value (binary)

            #to get printable (hex) value of digest use:
            print unpack('H*', $digest_value);

       o   X509_issuer_and_serial_hash

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sort of a checksum of issuer name and serial number of X509
           certificate $x.  The result is not a full hash (e.g. sha-1), it is
           kind-of-a-hash truncated to the size of 'unsigned long' (32 bits).
           The resulting value might differ across different openssl versions
           for the same X509 certificate.

            my $rv = Net::SSLeay::X509_issuer_and_serial_hash($x);
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: number representing checksum

       o   X509_issuer_name_hash

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sort of a checksum of issuer name of X509 certificate $x.  The
           result is not a full hash (e.g. sha-1), it is kind-of-a-hash
           truncated to the size of 'unsigned long' (32 bits).  The resulting
           value might differ across different openssl versions for the same
           X509 certificate.

            my $rv = Net::SSLeay::X509_issuer_name_hash($x);
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: number representing checksum

       o   X509_subject_name_hash

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sort of a checksum of subject name of X509 certificate $x.  The
           result is not a full hash (e.g. sha-1), it is kind-of-a-hash
           truncated to the size of 'unsigned long' (32 bits).  The resulting
           value might differ across different openssl versions for the same
           X509 certificate.

            my $rv = Net::SSLeay::X509_subject_name_hash($x);
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: number representing checksum

       o   X509_pubkey_digest

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.7

           Computes digest/fingerprint of public key from X509 certificate
           $data using $type hash function.

            my $digest_value = Net::SSLeay::X509_pubkey_digest($data, $type);
            # $data - value corresponding to openssl's X509 structure
            # $type - value corresponding to openssl's EVP_MD structure - e.g. got via EVP_get_digestbyname()
            #
            # returns: hash value (binary)

            #to get printable (hex) value of digest use:
            print unpack('H*', $digest_value);

       o   X509_set_issuer_name

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets issuer of X509 certificate $x to $name.

            my $rv = Net::SSLeay::X509_set_issuer_name($x, $name);
            # $x - value corresponding to openssl's X509 structure
            # $name - value corresponding to openssl's X509_NAME structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_set_pubkey

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets public key of X509 certificate $x to $pkey.

            my $rv = Net::SSLeay::X509_set_pubkey($x, $pkey);
            # $x - value corresponding to openssl's X509 structure
            # $pkey - value corresponding to openssl's EVP_PKEY structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_set_serialNumber

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets serial number of X509 certificate $x to $serial.

            my $rv = Net::SSLeay::X509_set_serialNumber($x, $serial);
            # $x - value corresponding to openssl's X509 structure
            # $serial - value corresponding to openssl's ASN1_INTEGER structure
            #
            # returns: 1 on success, 0 on failure

            #to create $serial value use one of these:
            $serial = Net::SSLeay::P_ASN1_INTEGER_set_hex('45ad6f');
            $serial = Net::SSLeay::P_ASN1_INTEGER_set_dec('7896541238529631478');
            $serial = Net::SSLeay::ASN1_INTEGER_set(45896);

       o   X509_set_subject_name

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets subject of X509 certificate $x to $name.

            my $rv = Net::SSLeay::X509_set_subject_name($x, $name);
            # $x - value corresponding to openssl's X509 structure
            # $name - value corresponding to openssl's X509_NAME structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_set_version

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Set 'version' value for X509 certificate $ to $version.

            my $rv = Net::SSLeay::X509_set_version($x, $version);
            # $x - value corresponding to openssl's X509 structure
            # $version - (integer) version number
            #
            # returns: 1 on success, 0 on failure

       o   X509_sign

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sign X509 certificate $x with private key $pkey (using digest
           algorithm $md).

            my $rv = Net::SSLeay::X509_sign($x, $pkey, $md);
            # $x - value corresponding to openssl's X509 structure
            # $pkey - value corresponding to openssl's EVP_PKEY structure
            # $md - value corresponding to openssl's EVP_MD structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_verify

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Verifies X509 object $a using public key $r (pubkey of issuing CA).

            my $rv = Net::SSLeay::X509_verify($x, $r);
            # $x - value corresponding to openssl's X509 structure
            # $r - value corresponding to openssl's EVP_PKEY structure
            #
            # returns: 0 - verify failure, 1 - verify OK, <0 - error

       o   X509_get_ext_count

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns the total number of extensions in X509 object $x.

            my $rv = Net::SSLeay::X509_get_ext_count($x);
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: count of extensions

       o   X509_get_pubkey

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns public key corresponding to given X509 object $x.

            my $rv = Net::SSLeay::X509_get_pubkey($x);
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: value corresponding to openssl's EVP_PKEY structure (0 on failure)

           NOTE: This method returns only the public key's key bits, without
           the algorithm or parameters.  Use "X509_get_X509_PUBKEY()" to
           return the full public key (SPKI) instead.

       o   X509_get_X509_PUBKEY

           COMPATIBILITY: not available in Net-SSLeay-1.72 and before

           Returns the full public key (SPKI) of given X509 certificate $x.

            Net::SSLeay::X509_get_X509_PUBKEY($x);
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: public key data in DER format (binary)

       o   X509_get_serialNumber

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns serial number of X509 certificate $x.

            my $rv = Net::SSLeay::X509_get_serialNumber($x);
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: value corresponding to openssl's ASN1_INTEGER structure (0 on failure)

           See "P_ASN1_INTEGER_get_dec", "P_ASN1_INTEGER_get_hex" or
           "ASN1_INTEGER_get" to decode ASN1_INTEGER object.

       o   X509_get_version

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns 'version' value of given X509 certificate $x.

            my $rv = Net::SSLeay::X509_get_version($x);
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: (integer) version

       o   X509_get_ext

           Returns X509_EXTENSION from $x509 based on given position/index.

            my $rv = Net::SSLeay::X509_get_ext($x509, $index);
            # $x509 - value corresponding to openssl's X509 structure
            # $index - (integer) position/index of extension within $x509
            #
            # returns: value corresponding to openssl's X509_EXTENSION structure (0 on failure)

       o   X509_get_ext_by_NID

           Returns X509_EXTENSION from $x509 based on given NID.

            my $rv = Net::SSLeay::X509_get_ext_by_NID($x509, $nid, $loc);
            # $x509 - value corresponding to openssl's X509 structure
            # $nid - (integer) NID value
            # $loc - (integer) position to start lookup at
            #
            # returns: position/index of extension, negative value on error
            #          call Net::SSLeay::X509_get_ext($x509, $rv) to get the actual extension

       o   X509_get_fingerprint

           Returns fingerprint of certificate $cert.

           NOTE: Does not exactly correspond to any low level API function.
           The implementation is basen on openssl's "X509_digest()".

            Net::SSLeay::X509_get_fingerprint($x509, $type);
            # $x509 - value corresponding to openssl's X509 structure
            # $type - (string) digest type, currently supported values:
            #         "md5"
            #         "sha1"
            #         "sha256"
            #         "ripemd160"
            #
            # returns: certificate digest - hexadecimal string (NOT binary data!)

       o   X509_get_issuer_name

           Return an X509_NAME object representing the issuer of the
           certificate $cert.

            my $rv = Net::SSLeay::X509_get_issuer_name($cert);
            # $cert - value corresponding to openssl's X509 structure
            #
            # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

       o   X509_get_notAfter

           Return an object giving the time after which the certificate $cert
           is not valid.

            my $rv = Net::SSLeay::X509_get_notAfter($cert);
            # $cert - value corresponding to openssl's X509 structure
            #
            # returns: value corresponding to openssl's ASN1_TIME structure (0 on failure)

           To get human readable/printable form the return value you can use:

            my $time = Net::SSLeay::X509_get_notAfter($cert);
            print "notAfter=", Net::SSLeay::P_ASN1_TIME_get_isotime($time), "\n";

       o   X509_get_notBefore

           Return an object giving the time before which the certificate $cert
           is not valid

            my $rv = Net::SSLeay::X509_get_notBefore($cert);
            # $cert - value corresponding to openssl's X509 structure
            #
            # returns: value corresponding to openssl's ASN1_TIME structure (0 on failure)

           To get human readable/printable form the return value you can use:

            my $time = Net::SSLeay::X509_get_notBefore($cert);
            print "notBefore=", Net::SSLeay::P_ASN1_TIME_get_isotime($time), "\n";

       o   X509_get_subjectAltNames

           NOTE: Does not exactly correspond to any low level API function.

           Returns the list of alternative subject names from X509 certificate
           $cert.

            my @rv = Net::SSLeay::X509_get_subjectAltNames($cert);
            # $cert - value corresponding to openssl's X509 structure
            #
            # returns: list containing pairs - name_type (integer), name_value (string)
            #          where name_type can be:
            #          0 - GEN_OTHERNAME
            #          1 - GEN_EMAIL
            #          2 - GEN_DNS
            #          3 - GEN_X400
            #          4 - GEN_DIRNAME
            #          5 - GEN_EDIPARTY
            #          6 - GEN_URI
            #          7 - GEN_IPADD
            #          8 - GEN_RID

           Note: type 7 - GEN_IPADD contains the IP address as a packed binary
           address.

       o   X509_get_subject_name

           Returns the subject of the certificate $cert.

            my $rv = Net::SSLeay::X509_get_subject_name($cert);
            # $cert - value corresponding to openssl's X509 structure
            #
            # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

       o   X509_gmtime_adj

           Adjust th ASN1_TIME object to the timestamp (in GMT).

            my $rv = Net::SSLeay::X509_gmtime_adj($s, $adj);
            # $s - value corresponding to openssl's ASN1_TIME structure
            # $adj - timestamp (seconds since 1.1.1970)
            #
            # returns: value corresponding to openssl's ASN1_TIME structure (0 on failure)

           BEWARE: this function may fail for dates after 2038 as it is
           dependent on time_t size on your system (32bit time_t does not work
           after 2038). Consider using "P_ASN1_TIME_set_isotime" instead).

       o   X509_load_cert_crl_file

           Takes PEM file and loads all X509 certificates and X509 CRLs from
           that file into X509_LOOKUP structure.

            my $rv = Net::SSLeay::X509_load_cert_crl_file($ctx, $file, $type);
            # $ctx - value corresponding to openssl's X509_LOOKUP structure
            # $file - (string) file name
            # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
            #                          if not FILETYPE_PEM then behaves as Net::SSLeay::X509_load_cert_file()
            #
            # returns: 1 on success, 0 on failure

       o   X509_load_cert_file

           Loads/adds X509 certificate from $file to X509_LOOKUP structure

            my $rv = Net::SSLeay::X509_load_cert_file($ctx, $file, $type);
            # $ctx - value corresponding to openssl's X509_LOOKUP structure
            # $file - (string) file name
            # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
            #
            # returns: 1 on success, 0 on failure

       o   X509_load_crl_file

           Loads/adds X509 CRL from $file to X509_LOOKUP structure

            my $rv = Net::SSLeay::X509_load_crl_file($ctx, $file, $type);
            # $ctx - value corresponding to openssl's X509_LOOKUP structure
            # $file - (string) file name
            # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
            #
            # returns: 1 on success, 0 on failure

       o   X509_policy_level_get0_node

           ??? (more info needed)

            my $rv = Net::SSLeay::X509_policy_level_get0_node($level, $i);
            # $level - value corresponding to openssl's X509_POLICY_LEVEL structure
            # $i - (integer) index/position
            #
            # returns: value corresponding to openssl's X509_POLICY_NODE structure (0 on failure)

       o   X509_policy_level_node_count

           ??? (more info needed)

            my $rv = Net::SSLeay::X509_policy_level_node_count($level);
            # $level - value corresponding to openssl's X509_POLICY_LEVEL structure
            #
            # returns: (integer) node count

       o   X509_policy_node_get0_parent

           ??? (more info needed)

            my $rv = Net::SSLeay::X509_policy_node_get0_parent($node);
            # $node - value corresponding to openssl's X509_POLICY_NODE structure
            #
            # returns: value corresponding to openssl's X509_POLICY_NODE structure (0 on failure)

       o   X509_policy_node_get0_policy

           ??? (more info needed)

            my $rv = Net::SSLeay::X509_policy_node_get0_policy($node);
            # $node - value corresponding to openssl's X509_POLICY_NODE structure
            #
            # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

       o   X509_policy_node_get0_qualifiers

           ??? (more info needed)

            my $rv = Net::SSLeay::X509_policy_node_get0_qualifiers($node);
            # $node - value corresponding to openssl's X509_POLICY_NODE structure
            #
            # returns: value corresponding to openssl's STACK_OF(POLICYQUALINFO) structure (0 on failure)

       o   X509_policy_tree_free

           ??? (more info needed)

            Net::SSLeay::X509_policy_tree_free($tree);
            # $tree - value corresponding to openssl's X509_POLICY_TREE structure
            #
            # returns: no return value

       o   X509_policy_tree_get0_level

           ??? (more info needed)

            my $rv = Net::SSLeay::X509_policy_tree_get0_level($tree, $i);
            # $tree - value corresponding to openssl's X509_POLICY_TREE structure
            # $i - (integer) level index
            #
            # returns: value corresponding to openssl's X509_POLICY_LEVEL structure (0 on failure)

       o   X509_policy_tree_get0_policies

           ??? (more info needed)

            my $rv = Net::SSLeay::X509_policy_tree_get0_policies($tree);
            # $tree - value corresponding to openssl's X509_POLICY_TREE structure
            #
            # returns: value corresponding to openssl's X509_POLICY_NODE structure (0 on failure)

       o   X509_policy_tree_get0_user_policies

           ??? (more info needed)

            my $rv = Net::SSLeay::X509_policy_tree_get0_user_policies($tree);
            # $tree - value corresponding to openssl's X509_POLICY_TREE structure
            #
            # returns: value corresponding to openssl's X509_POLICY_NODE structure (0 on failure)

       o   X509_policy_tree_level_count

           ??? (more info needed)

            my $rv = Net::SSLeay::X509_policy_tree_level_count($tree);
            # $tree - value corresponding to openssl's X509_POLICY_TREE structure
            #
            # returns: (integer) count

       o   X509_verify_cert_error_string

           Returns a human readable error string for verification error $n.

            my $rv = Net::SSLeay::X509_verify_cert_error_string($n);
            # $n - (long) numeric error code
            #
            # returns: error string

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_STORE_CTX_get_error.html>

       o   P_X509_add_extensions

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Adds one or more X509 extensions to X509 object $x.

            my $rv = Net::SSLeay::P_X509_add_extensions($x, $ca_cert, $nid, $value);
            # $x - value corresponding to openssl's X509 structure
            # $ca_cert - value corresponding to openssl's X509 structure (issuer's cert - necessary for sertting NID_authority_key_identifier)
            # $nid - NID identifying extension to be set
            # $value - extension value
            #
            # returns: 1 on success, 0 on failure

           You can set more extensions at once:

            my $rv = Net::SSLeay::P_X509_add_extensions($x509, $ca_cert,
                           &Net::SSLeay::NID_key_usage => 'digitalSignature,keyEncipherment',
                           &Net::SSLeay::NID_subject_key_identifier => 'hash',
                           &Net::SSLeay::NID_authority_key_identifier => 'keyid',
                           &Net::SSLeay::NID_authority_key_identifier => 'issuer',
                           &Net::SSLeay::NID_basic_constraints => 'CA:FALSE',
                           &Net::SSLeay::NID_ext_key_usage => 'serverAuth,clientAuth',
                           &Net::SSLeay::NID_netscape_cert_type => 'server',
                           &Net::SSLeay::NID_subject_alt_name => 'DNS:s1.dom.com,DNS:s2.dom.com,DNS:s3.dom.com',
                     );

       o   P_X509_copy_extensions

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Copies X509 extensions from X509_REQ object to X509 object - handy
           when you need to turn X509_REQ into X509 certificate.

            Net::SSLeay::P_X509_copy_extensions($x509_req, $x509, $override);
            # $x509_req - value corresponding to openssl's X509_REQ structure
            # $x509 - value corresponding to openssl's X509 structure
            # $override - (integer) flag indication whether to override already existing items in $x509 (default 1)
            #
            # returns: 1 on success, 0 on failure

       o   P_X509_get_crl_distribution_points

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.7

           Get the list of CRL distribution points from X509 certificate.

            my @cdp = Net::SSLeay::P_X509_get_crl_distribution_points($x509);
            # $x509 - value corresponding to openssl's X509 structure
            #
            # returns: list of distribution points (usually URLs)

       o   P_X509_get_ext_key_usage

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.7

           Gets the list of extended key usage of given X509 certificate
           $cert.

            my @ext_usage = Net::SSLeay::P_X509_get_ext_key_usage($cert, $format);
            # $cert - value corresponding to openssl's X509 structure
            # $format - choose type of return values: 0=OIDs, 1=NIDs, 2=shortnames, 3=longnames
            #
            # returns: list of values

           Examples:

            my @extkeyusage_oid = Net::SSLeay::P_X509_get_ext_key_usage($x509,0);
            # returns for example: ("1.3.6.1.5.5.7.3.1", "1.3.6.1.5.5.7.3.2")

            my @extkeyusage_nid = Net::SSLeay::P_X509_get_ext_key_usage($x509,1);
            # returns for example: (129, 130)

            my @extkeyusage_sn  = Net::SSLeay::P_X509_get_ext_key_usage($x509,2);
            # returns for example: ("serverAuth", "clientAuth")

            my @extkeyusage_ln  = Net::SSLeay::P_X509_get_ext_key_usage($x509,3);
            # returns for example: ("TLS Web Server Authentication",  "TLS Web Client Authentication")

       o   P_X509_get_key_usage

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Gets the list of key usage of given X509 certificate $cert.

            my @keyusage = Net::SSLeay::P_X509_get_key_usage($cert);
            # $cert - value corresponding to openssl's X509 structure
            #
            # returns: list of key usage values which can be none, one or more from the following list:
            #          "digitalSignature"
            #          "nonRepudiation"
            #          "keyEncipherment"
            #          "dataEncipherment"
            #          "keyAgreement"
            #          "keyCertSign"
            #          "cRLSign"
            #          "encipherOnly"
            #          "decipherOnly"

       o   P_X509_get_netscape_cert_type

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Gets the list of Netscape cert types of given X509 certificate
           $cert.

            Net::SSLeay::P_X509_get_netscape_cert_type($cert);
            # $cert - value corresponding to openssl's X509 structure
            #
            # returns: list of Netscape type values which can be none, one or more from the following list:
            #          "client"
            #          "server"
            #          "email"
            #          "objsign"
            #          "reserved"
            #          "sslCA"
            #          "emailCA"
            #          "objCA"

       o   P_X509_get_pubkey_alg

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns ASN1_OBJECT corresponding to X509 certificate public key
           algorithm.

            my $rv = Net::SSLeay::P_X509_get_pubkey_alg($x);
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

           To get textual representation use:

            my $alg = Net::SSLeay::OBJ_obj2txt(Net::SSLeay::P_X509_get_pubkey_alg($x509));
            # returns for example: "rsaEncryption"

       o   P_X509_get_signature_alg

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns ASN1_OBJECT corresponding to X509 signarite key algorithm.

            my $rv = Net::SSLeay::P_X509_get_signature_alg($x);
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

           To get textual representation use:

            my $alg = Net::SSLeay::OBJ_obj2txt(Net::SSLeay::P_X509_get_signature_alg($x509))
            # returns for example: "sha1WithRSAEncryption"

       Low level API: X509_REQ_* related functions

       o   X509_REQ_new

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Creates a new X509_REQ structure.

            my $rv = Net::SSLeay::X509_REQ_new();
            #
            # returns: value corresponding to openssl's X509_REQ structure (0 on failure)

       o   X509_REQ_free

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Free an allocated X509_REQ structure.

            Net::SSLeay::X509_REQ_free($x);
            # $x - value corresponding to openssl's X509_REQ structure
            #
            # returns: no return value

       o   X509_REQ_add1_attr_by_NID

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Adds an attribute whose name is defined by a NID $nid. The field
           value to be added is in $bytes.

            my $rv = Net::SSLeay::X509_REQ_add1_attr_by_NID($req, $nid, $type, $bytes);
            # $req - value corresponding to openssl's X509_REQ structure
            # $nid - (integer) NID value
            # $type - (integer) type of data in $bytes (see below)
            # $bytes - data to be set
            #
            # returns: 1 on success, 0 on failure

            # values for $type - use constants:
            &Net::SSLeay::MBSTRING_UTF8     - $bytes contains utf8 encoded data
            &Net::SSLeay::MBSTRING_ASC      - $bytes contains ASCII data

       o   X509_REQ_digest

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Computes digest/fingerprint of X509_REQ $data using $type hash
           function.

            my $digest_value = Net::SSLeay::X509_REQ_digest($data, $type);
            # $data - value corresponding to openssl's X509_REQ structure
            # $type - value corresponding to openssl's EVP_MD structure - e.g. got via EVP_get_digestbyname()
            #
            # returns: hash value (binary)

            #to get printable (hex) value of digest use:
            print unpack('H*', $digest_value);

       o   X509_REQ_get_attr_by_NID

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Retrieve the next index matching $nid after $lastpos ($lastpos
           should initially be set to -1).

            my $rv = Net::SSLeay::X509_REQ_get_attr_by_NID($req, $nid, $lastpos=-1);
            # $req - value corresponding to openssl's X509_REQ structure
            # $nid - (integer) NID value
            # $lastpos - [optional] (integer) index where to start search (default -1)
            #
            # returns: index (-1 if there are no more entries)

           Note: use "P_X509_REQ_get_attr" to get the actual attribute value -
           e.g.

            my $index = Net::SSLeay::X509_REQ_get_attr_by_NID($req, $nid);
            my @attr_values = Net::SSLeay::P_X509_REQ_get_attr($req, $index);

       o   X509_REQ_get_attr_by_OBJ

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Retrieve the next index matching $obj after $lastpos ($lastpos
           should initially be set to -1).

            my $rv = Net::SSLeay::X509_REQ_get_attr_by_OBJ($req, $obj, $lastpos=-1);
            # $req - value corresponding to openssl's X509_REQ structure
            # $obj - value corresponding to openssl's ASN1_OBJECT structure
            # $lastpos - [optional] (integer) index where to start search (default -1)
            #
            # returns: index (-1 if there are no more entries)

           Note: use "P_X509_REQ_get_attr" to get the actual attribute value -
           e.g.

            my $index = Net::SSLeay::X509_REQ_get_attr_by_NID($req, $nid);
            my @attr_values = Net::SSLeay::P_X509_REQ_get_attr($req, $index);

       o   X509_REQ_get_attr_count

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns the total number of attributes in $req.

            my $rv = Net::SSLeay::X509_REQ_get_attr_count($req);
            # $req - value corresponding to openssl's X509_REQ structure
            #
            # returns: (integer) items count

       o   X509_REQ_get_pubkey

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns public key corresponding to given X509_REQ object $x.

            my $rv = Net::SSLeay::X509_REQ_get_pubkey($x);
            # $x - value corresponding to openssl's X509_REQ structure
            #
            # returns: value corresponding to openssl's EVP_PKEY structure (0 on failure)

       o   X509_REQ_get_subject_name

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns X509_NAME object corresponding to subject name of given
           X509_REQ object $x.

            my $rv = Net::SSLeay::X509_REQ_get_subject_name($x);
            # $x - value corresponding to openssl's X509_REQ structure
            #
            # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

       o   X509_REQ_get_version

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns 'version' value for given X509_REQ object $x.

            my $rv = Net::SSLeay::X509_REQ_get_version($x);
            # $x - value corresponding to openssl's X509_REQ structure
            #
            # returns: (integer) version e.g. 0 = "version 1"

       o   X509_REQ_set_pubkey

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets public key of given X509_REQ object $x to $pkey.

            my $rv = Net::SSLeay::X509_REQ_set_pubkey($x, $pkey);
            # $x - value corresponding to openssl's X509_REQ structure
            # $pkey - value corresponding to openssl's EVP_PKEY structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_REQ_set_subject_name

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets subject name of given X509_REQ object $x to X509_NAME object
           $name.

            my $rv = Net::SSLeay::X509_REQ_set_subject_name($x, $name);
            # $x - value corresponding to openssl's X509_REQ structure
            # $name - value corresponding to openssl's X509_NAME structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_REQ_set_version

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets 'version' of given X509_REQ object $x to $version.

            my $rv = Net::SSLeay::X509_REQ_set_version($x, $version);
            # $x - value corresponding to openssl's X509_REQ structure
            # $version - (integer) e.g. 0 = "version 1"
            #
            # returns: 1 on success, 0 on failure

       o   X509_REQ_sign

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sign X509_REQ object $x with private key $pk (using digest
           algorithm $md).

            my $rv = Net::SSLeay::X509_REQ_sign($x, $pk, $md);
            # $x - value corresponding to openssl's X509_REQ structure
            # $pk - value corresponding to openssl's EVP_PKEY structure (requestor's private key)
            # $md - value corresponding to openssl's EVP_MD structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_REQ_verify

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Verifies X509_REQ object $x using public key $r (pubkey of
           requesting party).

            my $rv = Net::SSLeay::X509_REQ_verify($x, $r);
            # $x - value corresponding to openssl's X509_REQ structure
            # $r - value corresponding to openssl's EVP_PKEY structure
            #
            # returns: 0 - verify failure, 1 - verify OK, <0 - error

       o   P_X509_REQ_add_extensions

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Adds one or more X509 extensions to X509_REQ object $x.

            my $rv = Net::SSLeay::P_X509_REQ_add_extensions($x, $nid, $value);
            # $x - value corresponding to openssl's X509_REQ structure
            # $nid - NID identifying extension to be set
            # $value - extension value
            #
            # returns: 1 on success, 0 on failure

           You can set more extensions at once:

            my $rv = Net::SSLeay::P_X509_REQ_add_extensions($x509_req,
                       &Net::SSLeay::NID_key_usage => 'digitalSignature,keyEncipherment',
                       &Net::SSLeay::NID_basic_constraints => 'CA:FALSE',
                       &Net::SSLeay::NID_ext_key_usage => 'serverAuth,clientAuth',
                       &Net::SSLeay::NID_netscape_cert_type => 'server',
                       &Net::SSLeay::NID_subject_alt_name => 'DNS:s1.com,DNS:s2.com',
                       &Net::SSLeay::NID_crl_distribution_points => 'URI:http://pki.com/crl1,URI:http://pki.com/crl2',
                     );

       o   P_X509_REQ_get_attr

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.7

           Returns attribute value for X509_REQ's attribute at index $n.

            Net::SSLeay::P_X509_REQ_get_attr($req, $n);
            # $req - value corresponding to openssl's X509_REQ structure
            # $n - (integer) attribute index
            #
            # returns: value corresponding to openssl's ASN1_STRING structure

       Low level API: X509_CRL_* related functions

       o   X509_CRL_new

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Creates a new X509_CRL structure.

            my $rv = Net::SSLeay::X509_CRL_new();
            #
            # returns: value corresponding to openssl's X509_CRL structure (0 on failure)

       o   X509_CRL_free

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Free an allocated X509_CRL structure.

            Net::SSLeay::X509_CRL_free($x);
            # $x - value corresponding to openssl's X509_CRL structure
            #
            # returns: no return value

       o   X509_CRL_digest

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Computes digest/fingerprint of X509_CRL $data using $type hash
           function.

            my $digest_value = Net::SSLeay::X509_CRL_digest($data, $type);
            # $data - value corresponding to openssl's X509_CRL structure
            # $type - value corresponding to openssl's EVP_MD structure - e.g. got via EVP_get_digestbyname()
            #
            # returns: hash value (binary)

           Example:

            my $x509_crl
            my $md = Net::SSLeay::EVP_get_digestbyname("sha1");
            my $digest_value = Net::SSLeay::X509_CRL_digest($x509_crl, $md);
            #to get printable (hex) value of digest use:
            print "digest=", unpack('H*', $digest_value), "\n";

       o   X509_CRL_get_ext

           COMPATIBILITY: not available in Net-SSLeay-1.54 and before

           Returns X509_EXTENSION from $x509 based on given position/index.

            my $rv = Net::SSLeay::X509_CRL_get_ext($x509, $index);
            # $x509 - value corresponding to openssl's X509_CRL structure
            # $index - (integer) position/index of extension within $x509
            #
            # returns: value corresponding to openssl's X509_EXTENSION structure (0 on failure)

       o   X509_CRL_get_ext_by_NID

           COMPATIBILITY: not available in Net-SSLeay-1.54 and before

           Returns X509_EXTENSION from $x509 based on given NID.

            my $rv = Net::SSLeay::X509_CRL_get_ext_by_NID($x509, $nid, $loc);
            # $x509 - value corresponding to openssl's X509_CRL structure
            # $nid - (integer) NID value
            # $loc - (integer) position to start lookup at
            #
            # returns: position/index of extension, negative value on error
            #          call Net::SSLeay::X509_CRL_get_ext($x509, $rv) to get the actual extension

       o   X509_CRL_get_ext_count

           COMPATIBILITY: not available in Net-SSLeay-1.54 and before

           Returns the total number of extensions in X509_CRL object $x.

            my $rv = Net::SSLeay::X509_CRL_get_ext_count($x);
            # $x - value corresponding to openssl's X509_CRL structure
            #
            # returns: count of extensions

       o   X509_CRL_get_issuer

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns X509_NAME object corresponding to the issuer of X509_CRL
           $x.

            my $rv = Net::SSLeay::X509_CRL_get_issuer($x);
            # $x - value corresponding to openssl's X509_CRL structure
            #
            # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

           See other "X509_NAME_*" functions to get more info from X509_NAME
           structure.

       o   X509_CRL_get_lastUpdate

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns 'lastUpdate' date-time value of X509_CRL object $x.

            my $rv = Net::SSLeay::X509_CRL_get_lastUpdate($x);
            # $x - value corresponding to openssl's X509_CRL structure
            #
            # returns: value corresponding to openssl's ASN1_TIME structure (0 on failure)

       o   X509_CRL_get_nextUpdate

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns 'nextUpdate' date-time value of X509_CRL object $x.

            my $rv = Net::SSLeay::X509_CRL_get_nextUpdate($x);
            # $x - value corresponding to openssl's X509_CRL structure
            #
            # returns: value corresponding to openssl's ASN1_TIME structure (0 on failure)

       o   X509_CRL_get_version

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns 'version' value of given X509_CRL structure $x.

            my $rv = Net::SSLeay::X509_CRL_get_version($x);
            # $x - value corresponding to openssl's X509_CRL structure
            #
            # returns: (integer) version

       o   X509_CRL_set_issuer_name

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.7

           Sets the issuer of X509_CRL object $x to X509_NAME object $name.

            my $rv = Net::SSLeay::X509_CRL_set_issuer_name($x, $name);
            # $x - value corresponding to openssl's X509_CRL structure
            # $name - value corresponding to openssl's X509_NAME structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_CRL_set_lastUpdate

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.7

           Sets 'lastUpdate' value of X509_CRL object $x to $tm.

            my $rv = Net::SSLeay::X509_CRL_set_lastUpdate($x, $tm);
            # $x - value corresponding to openssl's X509_CRL structure
            # $tm - value corresponding to openssl's ASN1_TIME structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_CRL_set_nextUpdate

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.7

           Sets 'nextUpdate' value of X509_CRL object $x to $tm.

            my $rv = Net::SSLeay::X509_CRL_set_nextUpdate($x, $tm);
            # $x - value corresponding to openssl's X509_CRL structure
            # $tm - value corresponding to openssl's ASN1_TIME structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_CRL_set_version

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.7

           Sets 'version' value of given X509_CRL structure $x to $version.

            my $rv = Net::SSLeay::X509_CRL_set_version($x, $version);
            # $x - value corresponding to openssl's X509_CRL structure
            # $version - (integer) version number (1 = version 2 CRL)
            #
            # returns: 1 on success, 0 on failure

           Note that if you want to use any X509_CRL extension you need to set
           "version 2 CRL" - "Net::SSLeay::X509_CRL_set_version($x, 1)".

       o   X509_CRL_sign

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sign X509_CRL object $x with private key $pkey (using digest
           algorithm $md).

            my $rv = Net::SSLeay::X509_CRL_sign($x, $pkey, $md);
            # $x - value corresponding to openssl's X509_CRL structure
            # $pkey - value corresponding to openssl's EVP_PKEY structure
            # $md - value corresponding to openssl's EVP_MD structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_CRL_sort

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.7

           Sorts the data of X509_CRL object so it will be written in serial
           number order.

            my $rv = Net::SSLeay::X509_CRL_sort($x);
            # $x - value corresponding to openssl's X509_CRL structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_CRL_verify

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Verifies X509_CRL object $a using public key $r (pubkey of issuing
           CA).

            my $rv = Net::SSLeay::X509_CRL_verify($a, $r);
            # $a - value corresponding to openssl's X509_CRL structure
            # $r - value corresponding to openssl's EVP_PKEY structure
            #
            # returns: 0 - verify failure, 1 - verify OK, <0 - error

       o   P_X509_CRL_add_revoked_serial_hex

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.7

           Adds given serial number $serial_hex to X509_CRL object $crl.

            Net::SSLeay::P_X509_CRL_add_revoked_serial_hex($crl, $serial_hex, $rev_time, $reason_code, $comp_time);
            # $crl - value corresponding to openssl's X509_CRL structure
            # $serial_hex - string (hexadecimal) representation of serial number
            # $rev_time - (revocation time) value corresponding to openssl's ASN1_TIME structure
            # $reason_code - [optional] (integer) reason code (see below) - default 0
            # $comp_time - [optional] (compromise time) value corresponding to openssl's ASN1_TIME structure
            #
            # returns: no return value

            reason codes:
            0 - unspecified
            1 - keyCompromise
            2 - CACompromise
            3 - affiliationChanged
            4 - superseded
            5 - cessationOfOperation
            6 - certificateHold
            7 - removeFromCRL

       o   P_X509_CRL_get_serial

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.7

           Returns serial number of X509_CRL object.

            my $rv = Net::SSLeay::P_X509_CRL_get_serial($crl);
            # $crl - value corresponding to openssl's X509_CRL structure
            #
            # returns: value corresponding to openssl's ASN1_INTEGER structure (0 on failure)

       o   P_X509_CRL_set_serial

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.7

           Sets serial number of X509_CRL object to $crl_number.

            my $rv = Net::SSLeay::P_X509_CRL_set_serial($crl, $crl_number);
            # $crl - value corresponding to openssl's X509_CRL structure
            # $crl_number - value corresponding to openssl's ASN1_INTEGER structure
            #
            # returns: 1 on success, 0 on failure

       Low level API: X509_EXTENSION_* related functions

       o   X509_EXTENSION_get_critical

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns 'critical' flag of given X509_EXTENSION object $ex.

            my $rv = Net::SSLeay::X509_EXTENSION_get_critical($ex);
            # $ex - value corresponding to openssl's X509_EXTENSION structure
            #
            # returns: (integer) 1 - critical, 0 - noncritical

       o   X509_EXTENSION_get_data

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns value (raw data) of X509_EXTENSION object $ne.

            my $rv = Net::SSLeay::X509_EXTENSION_get_data($ne);
            # $ne - value corresponding to openssl's X509_EXTENSION structure
            #
            # returns: value corresponding to openssl's ASN1_OCTET_STRING structure (0 on failure)

           Note: you can use "P_ASN1_STRING_get" to convert ASN1_OCTET_STRING
           into perl scalar variable.

       o   X509_EXTENSION_get_object

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns OID (ASN1_OBJECT) of X509_EXTENSION object $ne.

            my $rv = Net::SSLeay::X509_EXTENSION_get_object($ex);
            # $ex - value corresponding to openssl's X509_EXTENSION structure
            #
            # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

       o   X509V3_EXT_print

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns string representation of given X509_EXTENSION object $ext.

            Net::SSLeay::X509V3_EXT_print($ext, $flags, $utf8_decode);
            # $ext - value corresponding to openssl's X509_EXTENSION structure
            # $flags - [optional] (integer) Currently the flag argument is unused and should be set to 0
            # $utf8_decode - [optional] 0 or 1 whether the returned value should be utf8 decoded (default=0)
            #
            # returns: no return value

       o   X509V3_EXT_d2i

           Parses an extension and returns its internal structure.

            my $rv = Net::SSLeay::X509V3_EXT_d2i($ext);
            # $ext - value corresponding to openssl's X509_EXTENSION structure
            #
            # returns: pointer ???

       Low level API: X509_NAME_* related functions

       o   X509_NAME_ENTRY_get_data

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Retrieves the field value of $ne in and ASN1_STRING structure.

            my $rv = Net::SSLeay::X509_NAME_ENTRY_get_data($ne);
            # $ne - value corresponding to openssl's X509_NAME_ENTRY structure
            #
            # returns: value corresponding to openssl's ASN1_STRING structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_NAME_ENTRY_get_object.html>

       o   X509_NAME_ENTRY_get_object

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Retrieves the field name of $ne in and ASN1_OBJECT structure.

            my $rv = Net::SSLeay::X509_NAME_ENTRY_get_object($ne);
            # $ne - value corresponding to openssl's X509_NAME_ENTRY structure
            #
            # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_NAME_ENTRY_get_object.html>

       o   X509_NAME_new

           COMPATIBILITY: not available in Net-SSLeay-1.55 and before;
           requires at least openssl-0.9.5

           Creates a new X509_NAME structure.  Adds a field whose name is
           defined by a string $field. The field value to be added is in
           $bytes.

            my $rv = Net::SSLeay::X509_NAME_new();
            #
            # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

       o   X509_NAME_hash

           COMPATIBILITY: not available in Net-SSLeay-1.55 and before;
           requires at least openssl-0.9.5

           Sort of a checksum of issuer name $name.  The result is not a full
           hash (e.g. sha-1), it is kind-of-a-hash truncated to the size of
           'unsigned long' (32 bits).  The resulting value might differ across
           different openssl versions for the same X509 certificate.

            my $rv = Net::SSLeay::X509_NAME_hash($name);
            # $name - value corresponding to openssl's X509_NAME structure
            #
            # returns: number representing checksum

       o   X509_NAME_add_entry_by_txt

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.5

           Adds a field whose name is defined by a string $field. The field
           value to be added is in $bytes.

            my $rv = Net::SSLeay::X509_NAME_add_entry_by_txt($name, $field, $type, $bytes, $len, $loc, $set);
            # $name - value corresponding to openssl's X509_NAME structure
            # $field - (string) field definition (name) - e.g. "organizationName"
            # $type - (integer) type of data in $bytes (see below)
            # $bytes - data to be set
            # $loc - [optional] (integer) index where the new entry is inserted: if it is -1 (default) it is appended
            # $set - [optional] (integer) determines how the new type is added. If it is 0 (default) a new RDN is created
            #
            # returns: 1 on success, 0 on failure

            # values for $type - use constants:
            &Net::SSLeay::MBSTRING_UTF8     - $bytes contains utf8 encoded data
            &Net::SSLeay::MBSTRING_ASC      - $bytes contains ASCII data

           Unicode note: when passing non-ascii (unicode) string in $bytes do
           not forget to set "$flags = &Net::SSLeay::MBSTRING_UTF8" and encode
           the perl $string via "$bytes = encode('utf-8', $string)".

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_NAME_add_entry_by_txt.html>

       o   X509_NAME_add_entry_by_NID

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.5

           Adds a field whose name is defined by a NID $nid. The field value
           to be added is in $bytes.

            my $rv = Net::SSLeay::X509_NAME_add_entry_by_NID($name, $nid, $type, $bytes, $len, $loc, $set);
            # $name - value corresponding to openssl's X509_NAME structure
            # $nid - (integer) field definition - NID value
            # $type - (integer) type of data in $bytes (see below)
            # $bytes - data to be set
            # $loc - [optional] (integer) index where the new entry is inserted: if it is -1 (default) it is appended
            # $set - [optional] (integer) determines how the new type is added. If it is 0 (default) a new RDN is created
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_NAME_add_entry_by_txt.html>

       o   X509_NAME_add_entry_by_OBJ

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-0.9.5

           Adds a field whose name is defined by a object (OID) $obj . The
           field value to be added is in $bytes.

            my $rv = Net::SSLeay::X509_NAME_add_entry_by_OBJ($name, $obj, $type, $bytes, $len, $loc, $set);
            # $name - value corresponding to openssl's X509_NAME structure
            # $obj - field definition - value corresponding to openssl's ASN1_OBJECT structure
            # $type - (integer) type of data in $bytes (see below)
            # $bytes - data to be set
            # $loc - [optional] (integer) index where the new entry is inserted: if it is -1 (default) it is appended
            # $set - [optional] (integer) determines how the new type is added. If it is 0 (default) a new RDN is created
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_NAME_add_entry_by_txt.html>

       o   X509_NAME_cmp

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Compares two X509_NAME obejcts.

            my $rv = Net::SSLeay::X509_NAME_cmp($a, $b);
            # $a - value corresponding to openssl's X509_NAME structure
            # $b - value corresponding to openssl's X509_NAME structure
            #
            # returns: 0 if $a matches $b; non zero otherwise

       o   X509_NAME_digest

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Computes digest/fingerprint of X509_NAME $data using $type hash
           function.

            my $digest_value = Net::SSLeay::X509_NAME_digest($data, $type);
            # $data - value corresponding to openssl's X509_NAME structure
            # $type - value corresponding to openssl's EVP_MD structure - e.g. got via EVP_get_digestbyname()
            #
            # returns: hash value (binary)

            #to get printable (hex) value of digest use:
            print unpack('H*', $digest_value);

       o   X509_NAME_entry_count

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns the total number of entries in $name.

            my $rv = Net::SSLeay::X509_NAME_entry_count($name);
            # $name - value corresponding to openssl's X509_NAME structure
            #
            # returns: (integer) entries count

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_NAME_get_index_by_NID.html>

       o   X509_NAME_get_entry

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Retrieves the X509_NAME_ENTRY from $name corresponding to index
           $loc. Acceptable values for $loc run from 0 to
           "Net::SSLeay::X509_NAME_entry_count($name)- 1". The value returned
           is an internal pointer which must not be freed.

            my $rv = Net::SSLeay::X509_NAME_get_entry($name, $loc);
            # $name - value corresponding to openssl's X509_NAME structure
            # $loc - (integer) index of wanted entry
            #
            # returns: value corresponding to openssl's X509_NAME_ENTRY structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_NAME_get_index_by_NID.html>

       o   X509_NAME_print_ex

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns a string with human readable version of $name.

            Net::SSLeay::X509_NAME_print_ex($name, $flags, $utf8_decode);
            # $name - value corresponding to openssl's X509_NAME structure
            # $flags - [optional] conversion flags (default XN_FLAG_RFC2253) - see below
            # $utf8_decode - [optional] 0 or 1 whether the returned value should be utf8 decoded (default=0)
            #
            # returns: string representation of $name

            #available conversion flags - use constants:
            &Net::SSLeay::XN_FLAG_COMPAT
            &Net::SSLeay::XN_FLAG_DN_REV
            &Net::SSLeay::XN_FLAG_DUMP_UNKNOWN_FIELDS
            &Net::SSLeay::XN_FLAG_FN_ALIGN
            &Net::SSLeay::XN_FLAG_FN_LN
            &Net::SSLeay::XN_FLAG_FN_MASK
            &Net::SSLeay::XN_FLAG_FN_NONE
            &Net::SSLeay::XN_FLAG_FN_OID
            &Net::SSLeay::XN_FLAG_FN_SN
            &Net::SSLeay::XN_FLAG_MULTILINE
            &Net::SSLeay::XN_FLAG_ONELINE
            &Net::SSLeay::XN_FLAG_RFC2253
            &Net::SSLeay::XN_FLAG_SEP_COMMA_PLUS
            &Net::SSLeay::XN_FLAG_SEP_CPLUS_SPC
            &Net::SSLeay::XN_FLAG_SEP_MASK
            &Net::SSLeay::XN_FLAG_SEP_MULTILINE
            &Net::SSLeay::XN_FLAG_SEP_SPLUS_SPC
            &Net::SSLeay::XN_FLAG_SPC_EQ

           Most likely you will be fine with default:

            Net::SSLeay::X509_NAME_print_ex($name, &Net::SSLeay::XN_FLAG_RFC2253);

           Or you might want RFC2253-like output without utf8 chars escaping:

            use Net::SSLeay qw/XN_FLAG_RFC2253 ASN1_STRFLGS_ESC_MSB/;
            my $flag_rfc22536_utf8 = (XN_FLAG_RFC2253) & (~ ASN1_STRFLGS_ESC_MSB);
            my $result = Net::SSLeay::X509_NAME_print_ex($name, $flag_rfc22536_utf8, 1);

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_NAME_print_ex.html>

       o   X509_NAME_get_text_by_NID

           Retrieves the text from the first entry in name which matches $nid,
           if no such entry exists -1 is returned.

           openssl note: this is a legacy function which has various
           limitations which makes it of minimal use in practice. It can only
           find the first matching entry and will copy the contents of the
           field verbatim: this can be highly confusing if the target is a
           multicharacter string type like a BMPString or a UTF8String.

            Net::SSLeay::X509_NAME_get_text_by_NID($name, $nid);
            # $name - value corresponding to openssl's X509_NAME structure
            # $nid - NID value (integer)
            #
            # returns: text value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_NAME_get_index_by_NID.html>

       o   X509_NAME_oneline

           Return an ASCII version of $name.

            Net::SSLeay::X509_NAME_oneline($name);
            # $name - value corresponding to openssl's X509_NAME structure
            #
            # returns: (string) ASCII version of $name

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_NAME_print_ex.html>

       o   sk_X509_NAME_free

           Free an allocated STACK_OF(X509_NAME) structure.

            Net::SSLeay::sk_X509_NAME_free($sk);
            # $sk - value corresponding to openssl's STACK_OF(X509_NAME) structure
            #
            # returns: no return value

       o   sk_X509_NAME_num

           Return number of items in STACK_OF(X509_NAME)

            my $rv = Net::SSLeay::sk_X509_NAME_num($sk);
            # $sk - value corresponding to openssl's STACK_OF(X509_NAME) structure
            #
            # returns: number of items

       o   sk_X509_NAME_value

           Returns X509_NAME from position $index in STACK_OF(X509_NAME)

            my $rv = Net::SSLeay::sk_X509_NAME_value($sk, $i);
            # $sk - value corresponding to openssl's STACK_OF(X509_NAME) structure
            # $i - (integer) index/position
            #
            # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

       o   add_file_cert_subjects_to_stack

           Add a file of certs to a stack. All certs in $file that are not
           already in the $stackCAs will be added.

            my $rv = Net::SSLeay::add_file_cert_subjects_to_stack($stackCAs, $file);
            # $stackCAs - value corresponding to openssl's STACK_OF(X509_NAME) structure
            # $file - (string) filename
            #
            # returns: 1 on success, 0 on failure

       o   add_dir_cert_subjects_to_stack

           Add a directory of certs to a stack. All certs in $dir that are not
           already in the $stackCAs will be added.

            my $rv = Net::SSLeay::add_dir_cert_subjects_to_stack($stackCAs, $dir);
            # $stackCAs - value corresponding to openssl's STACK_OF(X509_NAME) structure
            # $dir - (string) the directory to append from. All files in this directory will be examined as potential certs. Any that are acceptable to SSL_add_dir_cert_subjects_to_stack() that are not already in the stack will be included.
            #
            # returns: 1 on success, 0 on failure

       Low level API: X509_STORE_* related functions

       o   X509_STORE_CTX_get_current_cert

           Returns the certificate in ctx which caused the error or 0 if no
           certificate is relevant.

            my $rv = Net::SSLeay::X509_STORE_CTX_get_current_cert($x509_store_ctx);
            # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
            #
            # returns: value corresponding to openssl's X509 structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_STORE_CTX_get_error.html>

       o   X509_STORE_CTX_get_error

           Returns the error code of $ctx.

            my $rv = Net::SSLeay::X509_STORE_CTX_get_error($x509_store_ctx);
            # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
            #
            # returns: (integer) error code

           For more info about erro code values check function
           "get_verify_result".

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_STORE_CTX_get_error.html>

       o   X509_STORE_CTX_get_error_depth

           Returns the depth of the error. This is a non-negative integer
           representing where in the certificate chain the error occurred. If
           it is zero it occurred in the end entity certificate, one if it is
           the certificate which signed the end entity certificate and so on.

            my $rv = Net::SSLeay::X509_STORE_CTX_get_error_depth($x509_store_ctx);
            # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
            #
            # returns: (integer) depth

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_STORE_CTX_get_error.html>

       o   X509_STORE_CTX_get_ex_data

           Is used to retrieve the information for $idx from $x509_store_ctx.

            my $rv = Net::SSLeay::X509_STORE_CTX_get_ex_data($x509_store_ctx, $idx);
            # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
            # $idx - (integer) index for application specific data
            #
            # returns: pointer to ???

       o   X509_STORE_CTX_set_ex_data

           Is used to store application data at arg for idx into
           $x509_store_ctx.

            my $rv = Net::SSLeay::X509_STORE_CTX_set_ex_data($x509_store_ctx, $idx, $data);
            # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
            # $idx - (integer) ???
            # $data - (pointer) ???
            #
            # returns: 1 on success, 0 on failure

       o   X509_STORE_CTX_set_cert

           Sets the certificate to be verified in $x509_store_ctx to $x.

            Net::SSLeay::X509_STORE_CTX_set_cert($x509_store_ctx, $x);
            # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_STORE_CTX_new.html>

       o   X509_STORE_CTX_set_error

           Sets the error code of $ctx to $s. For example it might be used in
           a verification callback to set an error based on additional checks.

            Net::SSLeay::X509_STORE_CTX_set_error($x509_store_ctx, $s);
            # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
            # $s - (integer) error id
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_STORE_CTX_get_error.html>

       o   X509_STORE_add_cert

           Adds X509 certificate $x into the X509_STORE $store.

            my $rv = Net::SSLeay::X509_STORE_add_cert($store, $x);
            # $store - value corresponding to openssl's X509_STORE structure
            # $x - value corresponding to openssl's X509 structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_STORE_add_crl

           Adds X509 CRL $x into the X509_STORE $store.

            my $rv = Net::SSLeay::X509_STORE_add_crl($store, $x);
            # $store - value corresponding to openssl's X509_STORE structure
            # $x - value corresponding to openssl's X509_CRL structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_STORE_set1_param

           ??? (more info needed)

            my $rv = Net::SSLeay::X509_STORE_set1_param($store, $pm);
            # $store - value corresponding to openssl's X509_STORE structure
            # $pm - value corresponding to openssl's X509_VERIFY_PARAM structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_STORE_set_flags

            Net::SSLeay::X509_STORE_set_flags($ctx, $flags);
            # $ctx - value corresponding to openssl's X509_STORE structure
            # $flags - (unsigned long) flags to be set (bitmask)
            #
            # returns: no return value

            #to create $flags value use:
            0x0001 - X509_V_FLAG_CB_ISSUER_CHECK - Send issuer+subject checks to verify_cb
            0x0002 - X509_V_FLAG_USE_CHECK_TIME - Use check time instead of current time
            0x0004 - X509_V_FLAG_CRL_CHECK - Lookup CRLs
            0x0008 - X509_V_FLAG_CRL_CHECK_ALL - Lookup CRLs for whole chain
            0x0010 - X509_V_FLAG_IGNORE_CRITICAL - Ignore unhandled critical extensions
            0x0020 - X509_V_FLAG_X509_STRICT - Disable workarounds for broken certificates
            0x0040 - X509_V_FLAG_ALLOW_PROXY_CERTS - Enable proxy certificate validation
            0x0080 - X509_V_FLAG_POLICY_CHECK - Enable policy checking
            0x0100 - X509_V_FLAG_EXPLICIT_POLICY - Policy variable require-explicit-policy
            0x0200 - X509_V_FLAG_INHIBIT_ANY - Policy variable inhibit-any-policy
            0x0400 - X509_V_FLAG_INHIBIT_MAP - Policy variable inhibit-policy-mapping
            0x0800 - X509_V_FLAG_NOTIFY_POLICY - Notify callback that policy is OK
            0x1000 - X509_V_FLAG_EXTENDED_CRL_SUPPORT - Extended CRL features such as indirect CRLs, alternate CRL signing keys
            0x2000 - X509_V_FLAG_USE_DELTAS - Delta CRL support
            0x4000 - X509_V_FLAG_CHECK_SS_SIGNATURE - Check selfsigned CA signature

            #or use corresponding constants like
            $flags = &Net::SSLeay::X509_V_FLAG_CB_ISSUER_CHECK;
            ...
            $flags = &Net::SSLeay::X509_V_FLAG_CHECK_SS_SIGNATURE;

       o   X509_STORE_set_purpose

            Net::SSLeay::X509_STORE_set_purpose($ctx, $purpose);
            # $ctx - value corresponding to openssl's X509_STORE structure
            # $purpose - (integer) purpose identifier
            #
            # returns: no return value

           For more details about $purpose identifier check "CTX_set_purpose".

       o   X509_STORE_set_trust

            Net::SSLeay::X509_STORE_set_trust($ctx, $trust);
            # $ctx - value corresponding to openssl's X509_STORE structure
            # $trust - (integer) trust identifier
            #
            # returns: no return value

           For more details about $trust identifier check "CTX_set_trust".

       Low level API: X509_VERIFY_PARAM_* related functions

       o   X509_VERIFY_PARAM_add0_policy

           Enables policy checking (it is disabled by default) and adds
           $policy to the acceptable policy set.

            my $rv = Net::SSLeay::X509_VERIFY_PARAM_add0_policy($param, $policy);
            # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
            # $policy - value corresponding to openssl's ASN1_OBJECT structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

       o   X509_VERIFY_PARAM_add0_table

           ??? (more info needed)

            my $rv = Net::SSLeay::X509_VERIFY_PARAM_add0_table($param);
            # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_VERIFY_PARAM_clear_flags

           Clears the flags $flags in param.

            my $rv = Net::SSLeay::X509_VERIFY_PARAM_clear_flags($param, $flags);
            # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
            # $flags - (unsigned long) flags to be set (bitmask)
            #
            # returns: 1 on success, 0 on failure

           For more details about $flags bitmask see "X509_STORE_set_flags".

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

       o   X509_VERIFY_PARAM_free

           Frees up the X509_VERIFY_PARAM structure.

            Net::SSLeay::X509_VERIFY_PARAM_free($param);
            # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
            #
            # returns: no return value

       o   X509_VERIFY_PARAM_get_depth

           Returns the current verification depth.

            my $rv = Net::SSLeay::X509_VERIFY_PARAM_get_depth($param);
            # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
            #
            # returns: (ineger) depth

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

       o   X509_VERIFY_PARAM_get_flags

           Returns the current verification flags.

            my $rv = Net::SSLeay::X509_VERIFY_PARAM_get_flags($param);
            # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
            #
            # returns: (unsigned long) flags to be set (bitmask)

           For more details about returned flags bitmask see
           "X509_STORE_set_flags".

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

       o   X509_VERIFY_PARAM_set_flags

            my $rv = Net::SSLeay::X509_VERIFY_PARAM_set_flags($param, $flags);
            # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
            # $flags - (unsigned long) flags to be set (bitmask)
            #
            # returns: 1 on success, 0 on failure

           For more details about $flags bitmask see "X509_STORE_set_flags".

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

       o   X509_VERIFY_PARAM_inherit

           ??? (more info needed)

            my $rv = Net::SSLeay::X509_VERIFY_PARAM_inherit($to, $from);
            # $to - value corresponding to openssl's X509_VERIFY_PARAM structure
            # $from - value corresponding to openssl's X509_VERIFY_PARAM structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_VERIFY_PARAM_lookup

           Finds X509_VERIFY_PARAM by name.

            my $rv = Net::SSLeay::X509_VERIFY_PARAM_lookup($name);
            # $name - (string) name we want to find
            #
            # returns: value corresponding to openssl's X509_VERIFY_PARAM structure (0 on failure)

       o   X509_VERIFY_PARAM_new

           Creates a new X509_VERIFY_PARAM structure.

            my $rv = Net::SSLeay::X509_VERIFY_PARAM_new();
            #
            # returns: value corresponding to openssl's X509_VERIFY_PARAM structure (0 on failure)

       o   X509_VERIFY_PARAM_set1

           Sets the name of X509_VERIFY_PARAM structure $to to the same value
           as the name of X509_VERIFY_PARAM structure $from.

            my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1($to, $from);
            # $to - value corresponding to openssl's X509_VERIFY_PARAM structure
            # $from - value corresponding to openssl's X509_VERIFY_PARAM structure
            #
            # returns: 1 on success, 0 on failure

       o   X509_VERIFY_PARAM_set1_name

           Sets the name of X509_VERIFY_PARAM structure $param to $name.

            my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1_name($param, $name);
            # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
            # $name - (string) name to be set
            #
            # returns: 1 on success, 0 on failure

       o   X509_VERIFY_PARAM_set1_policies

           Enables policy checking (it is disabled by default) and sets the
           acceptable policy set to policies.  Any existing policy set is
           cleared. The policies parameter can be 0 to clear an existing
           policy set.

            my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1_policies($param, $policies);
            # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
            # $policies - value corresponding to openssl's STACK_OF(ASN1_OBJECT) structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

       o   X509_VERIFY_PARAM_set_depth

           Sets the maximum verification depth to depth. That is the maximum
           number of untrusted CA certificates that can appear in a chain.

            Net::SSLeay::X509_VERIFY_PARAM_set_depth($param, $depth);
            # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
            # $depth - (integer) depth to be set
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

       o   X509_VERIFY_PARAM_set_purpose

           Sets the verification purpose in $param to $purpose. This
           determines the acceptable purpose of the certificate chain, for
           example SSL client or SSL server.

            my $rv = Net::SSLeay::X509_VERIFY_PARAM_set_purpose($param, $purpose);
            # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
            # $purpose - (integer) purpose identifier
            #
            # returns: 1 on success, 0 on failure

           For more details about $purpose identifier check "CTX_set_purpose".

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

       o   X509_VERIFY_PARAM_set_time

           Sets the verification time in $param to $t. Normally the current
           time is used.

            Net::SSLeay::X509_VERIFY_PARAM_set_time($param, $t);
            # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
            # $t - (time_t) time in seconds since 1.1.1970
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

       o   X509_VERIFY_PARAM_set_trust

           Sets the trust setting in $param to $trust.

            my $rv = Net::SSLeay::X509_VERIFY_PARAM_set_trust($param, $trust);
            # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
            # $trust - (integer) trust identifier
            #
            # returns: 1 on success, 0 on failure

           For more details about $trust identifier check "CTX_set_trust".

           Check openssl doc
           <http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

       o   X509_VERIFY_PARAM_table_cleanup

           ??? (more info needed)

            Net::SSLeay::X509_VERIFY_PARAM_table_cleanup();
            #
            # returns: no return value

       Low level API: Cipher (EVP_CIPHER_*) related functions

       o   EVP_get_cipherbyname

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns an EVP_CIPHER structure when passed a cipher name.

            my $rv = Net::SSLeay::EVP_get_cipherbyname($name);
            # $name - (string) cipher name e.g. 'aes-128-cbc', 'camellia-256-ecb', 'des-ede', ...
            #
            # returns: value corresponding to openssl's EVP_CIPHER structure

           Check openssl doc
           <http://www.openssl.org/docs/crypto/EVP_EncryptInit.html>

       Low level API: Digest (EVP_MD_*) related functions

       o   OpenSSL_add_all_digests

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

            Net::SSLeay::OpenSSL_add_all_digests();
            # no args, no return value

           http://www.openssl.org/docs/crypto/OpenSSL_add_all_algorithms.html

       o   P_EVP_MD_list_all

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before;
           requires at least openssl-1.0.0

           NOTE: Does not exactly correspond to any low level API function

            my $rv = Net::SSLeay::P_EVP_MD_list_all();
            #
            # returns: arrayref - list of available digest names

           The returned digest names correspond to values expected by
           "EVP_get_digestbyname".

           Note that some of the digests are available by default and some
           only after calling "OpenSSL_add_all_digests".

       o   EVP_get_digestbyname

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

            my $rv = Net::SSLeay::EVP_get_digestbyname($name);
            # $name - string with digest name
            #
            # returns: value corresponding to openssl's EVP_MD structure

           The $name param can be:

            md2
            md4
            md5
            mdc2
            ripemd160
            sha
            sha1
            sha224
            sha256
            sha512
            whirlpool

           Or better check the supported digests by calling
           "P_EVP_MD_list_all".

       o   EVP_MD_type

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

            my $rv = Net::SSLeay::EVP_MD_type($md);
            # $md - value corresponding to openssl's EVP_MD structure
            #
            # returns: the NID (integer) of the OBJECT IDENTIFIER representing the given message digest

       o   EVP_MD_size

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

            my $rv = Net::SSLeay::EVP_MD_size($md);
            # $md - value corresponding to openssl's EVP_MD structure
            #
            # returns: the size of the message digest in bytes (e.g. 20 for SHA1)

       o   EVP_MD_CTX_md

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before;
           requires at least openssl-0.9.7

            Net::SSLeay::EVP_MD_CTX_md($ctx);
            # $ctx - value corresponding to openssl's EVP_MD_CTX structure
            #
            # returns: value corresponding to openssl's EVP_MD structure

       o   EVP_MD_CTX_create

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before;
           requires at least openssl-0.9.7

           Allocates, initializes and returns a digest context.

            my $rv = Net::SSLeay::EVP_MD_CTX_create();
            #
            # returns: value corresponding to openssl's EVP_MD_CTX structure

           The complete idea behind EVP_MD_CTX looks like this example:

             Net::SSLeay::OpenSSL_add_all_digests();

             my $md = Net::SSLeay::EVP_get_digestbyname("sha1");
             my $ctx = Net::SSLeay::EVP_MD_CTX_create();
             Net::SSLeay::EVP_DigestInit($ctx, $md);

             while(my $chunk = get_piece_of_data()) {
               Net::SSLeay::EVP_DigestUpdate($ctx,$chunk);
             }

             my $result = Net::SSLeay::EVP_DigestFinal($ctx);
             Net::SSLeay::EVP_MD_CTX_destroy($ctx);

             print "digest=", unpack('H*', $result), "\n"; #print hex value

       o   EVP_DigestInit_ex

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before;
           requires at least openssl-0.9.7

           Sets up digest context $ctx to use a digest $type from ENGINE
           $impl, $ctx must be initialized before calling this function, type
           will typically be supplied by a function such as
           "EVP_get_digestbyname". If $impl is 0 then the default
           implementation of digest $type is used.

            my $rv = Net::SSLeay::EVP_DigestInit_ex($ctx, $type, $impl);
            # $ctx  - value corresponding to openssl's EVP_MD_CTX structure
            # $type - value corresponding to openssl's EVP_MD structure
            # $impl - value corresponding to openssl's ENGINE structure
            #
            # returns: 1 for success and 0 for failure

       o   EVP_DigestInit

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before;
           requires at least openssl-0.9.7

           Behaves in the same way as "EVP_DigestInit_ex" except the passed
           context $ctx does not have to be initialized, and it always uses
           the default digest implementation.

            my $rv = Net::SSLeay::EVP_DigestInit($ctx, $type);
            # $ctx - value corresponding to openssl's EVP_MD_CTX structure
            # $type - value corresponding to openssl's EVP_MD structure
            #
            # returns: 1 for success and 0 for failure

       o   EVP_MD_CTX_destroy

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before;
           requires at least openssl-0.9.7

           Cleans up digest context $ctx and frees up the space allocated to
           it, it should be called only on a context created using
           "EVP_MD_CTX_create".

            Net::SSLeay::EVP_MD_CTX_destroy($ctx);
            # $ctx - value corresponding to openssl's EVP_MD_CTX structure
            #
            # returns: no return value

       o   EVP_DigestUpdate

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before;
           requires at least openssl-0.9.7

            my $rv = Net::SSLeay::EVP_DigestUpdate($ctx, $data);
            # $ctx  - value corresponding to openssl's EVP_MD_CTX structure
            # $data - data to be hashed
            #
            # returns: 1 for success and 0 for failure

       o   EVP_DigestFinal_ex

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before;
           requires at least openssl-0.9.7

           Retrieves the digest value from $ctx. After calling
           "EVP_DigestFinal_ex" no additional calls to "EVP_DigestUpdate" can
           be made, but "EVP_DigestInit_ex" can be called to initialize a new
           digest operation.

            my $digest_value = Net::SSLeay::EVP_DigestFinal_ex($ctx);
            # $ctx - value corresponding to openssl's EVP_MD_CTX structure
            #
            # returns: hash value (binary)

            #to get printable (hex) value of digest use:
            print unpack('H*', $digest_value);

       o   EVP_DigestFinal

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before;
           requires at least openssl-0.9.7

           Similar to "EVP_DigestFinal_ex" except the digest context ctx is
           automatically cleaned up.

            my $rv = Net::SSLeay::EVP_DigestFinal($ctx);
            # $ctx - value corresponding to openssl's EVP_MD_CTX structure
            #
            # returns: hash value (binary)

            #to get printable (hex) value of digest use:
            print unpack('H*', $digest_value);

       o   MD2

           COMPATIBILITY: no supported by default in openssl-1.0.0

           Computes MD2 from given $data (all data needs to be loaded into
           memory)

            my $digest = Net::SSLeay::MD2($data);
            print "digest(hexadecimal)=", unpack('H*', $digest);

       o   MD4

           Computes MD4 from given $data (all data needs to be loaded into
           memory)

            my $digest = Net::SSLeay::MD4($data);
            print "digest(hexadecimal)=", unpack('H*', $digest);

       o   MD5

           Computes MD5 from given $data (all data needs to be loaded into
           memory)

            my $digest = Net::SSLeay::MD5($data);
            print "digest(hexadecimal)=", unpack('H*', $digest);

       o   RIPEMD160

           Computes RIPEMD160 from given $data (all data needs to be loaded
           into memory)

            my $digest = Net::SSLeay::RIPEMD160($data);
            print "digest(hexadecimal)=", unpack('H*', $digest);

       o   SHA1

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           Computes SHA1 from given $data (all data needs to be loaded into
           memory)

            my $digest = Net::SSLeay::SHA1($data);
            print "digest(hexadecimal)=", unpack('H*', $digest);

       o   SHA256

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before;
           requires at least openssl-0.9.8

           Computes SHA256 from given $data (all data needs to be loaded into
           memory)

            my $digest = Net::SSLeay::SHA256($data);
            print "digest(hexadecimal)=", unpack('H*', $digest);

       o   SHA512

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before;
           requires at least openssl-0.9.8

           Computes SHA512 from given $data (all data needs to be loaded into
           memory)

            my $digest = Net::SSLeay::SHA512($data);
            print "digest(hexadecimal)=", unpack('H*', $digest);

       o   EVP_Digest

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before;
           requires at least openssl-0.9.7

           Computes "any" digest from given $data (all data needs to be loaded
           into memory)

            my $md = Net::SSLeay::EVP_get_digestbyname("sha1"); #or any other algorithm
            my $digest = Net::SSLeay::EVP_Digest($data, $md);
            print "digest(hexadecimal)=", unpack('H*', $digest);

       o   EVP_sha1

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

            my $md = Net::SSLeay::EVP_sha1();
            #
            # returns: value corresponding to openssl's EVP_MD structure

       o   EVP_sha256

           COMPATIBILITY: requires at least openssl-0.9.8

            my $md = Net::SSLeay::EVP_sha256();
            #
            # returns: value corresponding to openssl's EVP_MD structure

       o   EVP_sha512

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before;
           requires at least openssl-0.9.8

            my $md = Net::SSLeay::EVP_sha512();
            #
            # returns: value corresponding to openssl's EVP_MD structure

       o   EVP_add_digest

            my $rv = Net::SSLeay::EVP_add_digest($digest);
            # $digest - value corresponding to openssl's EVP_MD structure
            #
            # returns: 1 on success, 0 otherwise

       Low level API: CIPHER_* related functions

       o   CIPHER_get_name

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           Returns name of the cipher used.

            my $rv = Net::SSLeay::CIPHER_description($cipher);
            # $cipher - value corresponding to openssl's SSL_CIPHER structure
            #
            # returns: (string) cipher name e.g. 'DHE-RSA-AES256-SHA'

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CIPHER_get_name.html>

           Example:

            my $ssl_cipher = Net::SSLeay::get_current_cipher($ssl);
            my $cipher_name = Net::SSLeay::CIPHER_get_name($ssl_cipher);

       o   CIPHER_description

           Returns a textual description of the cipher used.

           ??? (does this function really work?)

            my $rv = Net::SSLeay::CIPHER_description($cipher, $buf, $size);
            # $cipher - value corresponding to openssl's SSL_CIPHER structure
            # $bufer - (string/buffer) ???
            # $size - (integer) ???
            #
            # returns: (string) cipher description e.g. 'DHE-RSA-AES256-SHA SSLv3 Kx=DH Au=RSA Enc=AES(256) Mac=SHA1'

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CIPHER_get_name.html>

       o   CIPHER_get_bits

           Returns the number of secret bits used for cipher.

            my $rv = Net::SSLeay::CIPHER_get_bits($c);
            # $c - value corresponding to openssl's SSL_CIPHER structure
            #
            # returns: (integert) number of secret bits, 0 on error

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_CIPHER_get_name.html>

       Low level API: RSA_* related functions

       o   RSA_generate_key

           Generates a key pair and returns it in a newly allocated RSA
           structure.  The pseudo-random number generator must be seeded prior
           to calling RSA_generate_key.

            my $rv = Net::SSLeay::RSA_generate_key($bits, $e, $perl_cb, $perl_cb_arg);
            # $bits - (integer) modulus size in bits e.g. 512, 1024, 2048
            # $e - (integer) public exponent, an odd number, typically 3, 17 or 65537
            # $perl_cb - [optional] reference to perl callback function
            # $perl_cb_arg - [optional] data that will be passed to callback function when invoked
            #
            # returns: value corresponding to openssl's RSA structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/RSA_generate_key.html>

       o   RSA_free

           Frees the RSA structure and its components. The key is erased
           before the memory is returned to the system.

            Net::SSLeay::RSA_free($r);
            # $r - value corresponding to openssl's RSA structure
            #
            # returns: no return value

           Check openssl doc <http://www.openssl.org/docs/crypto/RSA_new.html>

       o   RSA_get_key_parameters

           Returns a list of pointers to BIGNUMs representing the parameters
           of the key in this order: (n, e, d, p, q, dmp1, dmq1, iqmp)
           Caution: returned list consists of SV pointers to BIGNUMs, which
           would need to be blessed as Crypt::OpenSSL::Bignum for further use

           my (@params) = RSA_get_key_parameters($r);

       Low level API: BIO_* related functions

       o   BIO_eof

           Returns 1 if the BIO has read EOF, the precise meaning of 'EOF'
           varies according to the BIO type.

            my $rv = Net::SSLeay::BIO_eof($s);
            # $s - value corresponding to openssl's BIO structure
            #
            # returns: 1 if EOF has been reached 0 otherwise

           Check openssl doc
           <http://www.openssl.org/docs/crypto/BIO_ctrl.html>

       o   BIO_f_ssl

           Returns the SSL BIO method. This is a filter BIO which is a wrapper
           round the OpenSSL SSL routines adding a BIO 'flavour' to SSL I/O.

            my $rv = Net::SSLeay::BIO_f_ssl();
            #
            # returns: value corresponding to openssl's BIO_METHOD structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/BIO_f_ssl.html>

       o   BIO_free

           Frees up a single BIO.

            my $rv = Net::SSLeay::BIO_free($bio;);
            # $bio; - value corresponding to openssl's BIO structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc <http://www.openssl.org/docs/crypto/BIO_new.html>

       o   BIO_new

           Returns a new BIO using method $type

            my $rv = Net::SSLeay::BIO_new($type);
            # $type - value corresponding to openssl's BIO_METHOD structure
            #
            # returns: value corresponding to openssl's BIO structure (0 on failure)

           Check openssl doc <http://www.openssl.org/docs/crypto/BIO_new.html>

       o   BIO_new_buffer_ssl_connect

           Creates a new BIO chain consisting of a buffering BIO, an SSL BIO
           (using ctx) and a connect BIO.

            my $rv = Net::SSLeay::BIO_new_buffer_ssl_connect($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: value corresponding to openssl's BIO structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/BIO_f_ssl.html>

       o   BIO_new_file

           Creates a new file BIO with mode $mode the meaning of mode is the
           same as the stdio function fopen(). The BIO_CLOSE flag is set on
           the returned BIO.

            my $rv = Net::SSLeay::BIO_new_file($filename, $mode);
            # $filename - (string) filename
            # $mode - (string) opening mode (as mode by stdio function fopen)
            #
            # returns: value corresponding to openssl's BIO structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/BIO_s_file.html>

       o   BIO_new_ssl

           Allocates an SSL BIO using SSL_CTX ctx and using client mode if
           client is non zero.

            my $rv = Net::SSLeay::BIO_new_ssl($ctx, $client);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $client - (integer) 0 or 1 - indicates ssl client mode
            #
            # returns: value corresponding to openssl's BIO structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/BIO_f_ssl.html>

       o   BIO_new_ssl_connect

           Creates a new BIO chain consisting of an SSL BIO (using ctx)
           followed by a connect BIO.

            my $rv = Net::SSLeay::BIO_new_ssl_connect($ctx);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            #
            # returns: value corresponding to openssl's BIO structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/BIO_f_ssl.html>

       o   BIO_pending

           Return the number of pending characters in the BIOs read buffers.

            my $rv = Net::SSLeay::BIO_pending($s);
            # $s - value corresponding to openssl's BIO structure
            #
            # returns: the amount of pending data

           Check openssl doc
           <http://www.openssl.org/docs/crypto/BIO_ctrl.html>

       o   BIO_wpending

           Return the number of pending characters in the BIOs write buffers.

            my $rv = Net::SSLeay::BIO_wpending($s);
            # $s - value corresponding to openssl's BIO structure
            #
            # returns: the amount of pending data

           Check openssl doc
           <http://www.openssl.org/docs/crypto/BIO_ctrl.html>

       o   BIO_read

           Read the underlying descriptor.

            Net::SSLeay::BIO_read($s, $max);
            # $s - value corresponding to openssl's BIO structure
            # $max - [optional] max. bytes to read (if not specified, the value 32768 is used)
            #
            # returns: data

           Check openssl doc
           <http://www.openssl.org/docs/crypto/BIO_read.html>

       o   BIO_write

           Attempts to write data from $buffer to BIO $b.

            my $rv = Net::SSLeay::BIO_write($b, $buffer);
            # $b - value corresponding to openssl's BIO structure
            # $buffer - data
            #
            # returns: amount of data successfully written
            #          or that no data was successfully read or written if the result is 0 or -1
            #          or -2 when the operation is not implemented in the specific BIO type

           Check openssl doc
           <http://www.openssl.org/docs/crypto/BIO_read.html>

       o   BIO_s_mem

           Return the memory BIO method function.

            my $rv = Net::SSLeay::BIO_s_mem();
            #
            # returns: value corresponding to openssl's BIO_METHOD structure (0 on failure)

           Check openssl doc
           <http://www.openssl.org/docs/crypto/BIO_s_mem.html>

       o   BIO_ssl_copy_session_id

           Copies an SSL session id between BIO chains from and to. It does
           this by locating the SSL BIOs in each chain and calling
           SSL_copy_session_id() on the internal SSL pointer.

            my $rv = Net::SSLeay::BIO_ssl_copy_session_id($to, $from);
            # $to - value corresponding to openssl's BIO structure
            # $from - value corresponding to openssl's BIO structure
            #
            # returns: 1 on success, 0 on failure

           Check openssl doc
           <http://www.openssl.org/docs/crypto/BIO_f_ssl.html>

       o   BIO_ssl_shutdown

           Closes down an SSL connection on BIO chain bio. It does this by
           locating the SSL BIO in the chain and calling SSL_shutdown() on its
           internal SSL pointer.

            Net::SSLeay::BIO_ssl_shutdown($ssl_bio);
            # $ssl_bio - value corresponding to openssl's BIO structure
            #
            # returns: no return value

           Check openssl doc
           <http://www.openssl.org/docs/crypto/BIO_f_ssl.html>

       Low level API: Server side Server Name Indication (SNI) support

       o   set_tlsext_host_name

           TBA

       o   get_servername

           TBA

       o   get_servername_type

           TBA

       o   CTX_set_tlsext_servername_callback

           COMPATIBILITY: requires at least OpenSSL 0.9.8f

           This function is used in a server to support Server side Server
           Name Indication (SNI).

            Net::SSLeay::CTX_set_tlsext_servername_callback($ctx, $code)
            # $ctx - SSL context
            # $code - reference to a subroutine that will be called when a new connection is being initiated
            #
            # returns: no return value
           On the client side:
           use set_tlsext_host_name($ssl, $servername) before initiating the SSL connection.

           On the server side: Set up an additional SSL_CTX() for each
           different certificate;

           Add a servername callback to each SSL_CTX() using
           CTX_set_tlsext_servername_callback();

           The callback function is required to retrieve the client-supplied
           servername with get_servername(ssl). Figure out the right SSL_CTX
           to go with that host name, then switch the SSL object to that
           SSL_CTX with set_SSL_CTX().

           Example:

            # set callback
            Net::SSLeay::CTX_set_tlsext_servername_callback($ctx,
               sub {
                 my $ssl = shift;
                 my $h = Net::SSLeay::get_servername($ssl);
                 Net::SSLeay::set_SSL_CTX($ssl, $hostnames{$h}->{ctx}) if exists $hostnames{$h};
               } );

           More complete example:

            # ... initialize Net::SSLeay

            my %hostnames = (
              'sni1' => { cert=>'sni1.pem', key=>'sni1.key' },
              'sni2' => { cert=>'sni2.pem', key=>'sni2.key' },
            );

            # create a new context for each certificate/key pair
            for my $name (keys %hostnames) {
              $hostnames{$name}->{ctx} = Net::SSLeay::CTX_new or die;
              Net::SSLeay::CTX_set_cipher_list($hostnames{$name}->{ctx}, 'ALL');
              Net::SSLeay::set_cert_and_key($hostnames{$name}->{ctx},
              $hostnames{$name}->{cert}, $hostnames{$name}->{key}) or die;
            }

            # create default context
            my $ctx = Net::SSLeay::CTX_new or die;
            Net::SSLeay::CTX_set_cipher_list($ctx, 'ALL');
            Net::SSLeay::set_cert_and_key($ctx, 'cert.pem','key.pem') or die;

            # set callback
            Net::SSLeay::CTX_set_tlsext_servername_callback($ctx, sub {
              my $ssl = shift;
              my $h = Net::SSLeay::get_servername($ssl);
              Net::SSLeay::set_SSL_CTX($ssl, $hostnames{$h}->{ctx}) if exists $hostnames{$h};
              } );

            # ... later

            $s = Net::SSLeay::new($ctx);
            Net::SSLeay::set_fd($s, fileno($accepted_socket));
            Net::SSLeay::accept($s);

       Low level API: NPN (next protocol negotiation) related functions

       NPN is being replaced with ALPN, a more recent TLS extension for
       application protocol negotiation that's in process of being adopted by
       IETF. Please look below for APLN API description.

       Simple approach for using NPN support looks like this:

        ### client side
        use Net::SSLeay;
        use IO::Socket::INET;

        Net::SSLeay::initialize();
        my $sock = IO::Socket::INET->new(PeerAddr=>'encrypted.google.com:443') or die;
        my $ctx = Net::SSLeay::CTX_tlsv1_new() or die;
        Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL);
        Net::SSLeay::CTX_set_next_proto_select_cb($ctx, ['http1.1','spdy/2']);
        my $ssl = Net::SSLeay::new($ctx) or die;
        Net::SSLeay::set_fd($ssl, fileno($sock)) or die;
        Net::SSLeay::connect($ssl);

        warn "client:negotiated=",Net::SSLeay::P_next_proto_negotiated($ssl), "\n";
        warn "client:last_status=", Net::SSLeay::P_next_proto_last_status($ssl), "\n";

        ### server side
        use Net::SSLeay;
        use IO::Socket::INET;

        Net::SSLeay::initialize();
        my $ctx = Net::SSLeay::CTX_tlsv1_new() or die;
        Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL);
        Net::SSLeay::set_cert_and_key($ctx, "t/data/cert.pem", "t/data/key.pem");
        Net::SSLeay::CTX_set_next_protos_advertised_cb($ctx, ['spdy/2','http1.1']);
        my $sock = IO::Socket::INET->new(LocalAddr=>'localhost', LocalPort=>5443, Proto=>'tcp', Listen=>20) or die;

        while (1) {
          my $ssl = Net::SSLeay::new($ctx);
          warn("server:waiting for incoming connection...\n");
          my $fd = $sock->accept();
          Net::SSLeay::set_fd($ssl, $fd->fileno);
          Net::SSLeay::accept($ssl);
          warn "server:negotiated=",Net::SSLeay::P_next_proto_negotiated($ssl),"\n";
          my $got = Net::SSLeay::read($ssl);
          Net::SSLeay::ssl_write_all($ssl, "length=".length($got));
          Net::SSLeay::free($ssl);
          $fd->close();
        }
        # check with: openssl s_client -connect localhost:5443 -nextprotoneg http/1.1,spdy/2

       Please note that the selection (negotiation) is performed by client
       side, the server side simply advertise the list of supported protocols.

       Advanced approach allows you to implement your own negotiation
       algorithm.

        #see below documentation for:
        Net::SSleay::CTX_set_next_proto_select_cb($ctx, $perl_callback_function, $callback_data);
        Net::SSleay::CTX_set_next_protos_advertised_cb($ctx, $perl_callback_function, $callback_data);

       Detection of NPN support (works even in older Net::SSLeay versions):

        use Net::SSLeay;

        if (exists &Net::SSLeay::P_next_proto_negotiated) {
          # do NPN stuff
        }

       o   CTX_set_next_proto_select_cb

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-1.0.1

           NOTE: You need CTX_set_next_proto_select_cb on client side of SSL
           connection.

           Simple usage - in this case a "common" negotiation algorithm (as
           implemented by openssl's function SSL_select_next_proto) is used.

            $rv = Net::SSleay::CTX_set_next_proto_select_cb($ctx, $arrayref);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $arrayref - list of accepted protocols - e.g. ['http1.0', 'http1.1']
            #
            # returns: 0 on success, 1 on failure

           Advanced usage (you probably do not need this):

            $rv = Net::SSleay::CTX_set_next_proto_select_cb($ctx, $perl_callback_function, $callback_data);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $perl_callback_function - reference to perl function
            # $callback_data - [optional] data to passed to callback function when invoked
            #
            # returns: 0 on success, 1 on failure

            # where callback function looks like
            sub npn_advertised_cb_invoke {
              my ($ssl, $arrayref_proto_list_advertised_by_server, $callback_data) = @_;
              my $status;
              # ...
              $status = 1;   #status can be:
                             # 0 - OPENSSL_NPN_UNSUPPORTED
                             # 1 - OPENSSL_NPN_NEGOTIATED
                             # 2 - OPENSSL_NPN_NO_OVERLAP
              return $status, ['http1.1','spdy/2']; # the callback has to return 2 values
            }

           To undefine/clear this callback use:

            Net::SSleay::CTX_set_next_proto_select_cb($ctx, undef);

       o   CTX_set_next_protos_advertised_cb

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-1.0.1

           NOTE: You need CTX_set_next_proto_select_cb on server side of SSL
           connection.

           Simple usage:

            $rv = Net::SSleay::CTX_set_next_protos_advertised_cb($ctx, $arrayref);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $arrayref - list of advertised protocols - e.g. ['http1.0', 'http1.1']
            #
            # returns: 0 on success, 1 on failure

           Advanced usage (you probably do not need this):

            $rv = Net::SSleay::CTX_set_next_protos_advertised_cb($ctx, $perl_callback_function, $callback_data);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $perl_callback_function - reference to perl function
            # $callback_data - [optional] data to passed to callback function when invoked
            #
            # returns: 0 on success, 1 on failure

            # where callback function looks like
            sub npn_advertised_cb_invoke {
              my ($ssl, $callback_data) = @_;
              # ...
              return ['http1.1','spdy/2']; # the callback has to return arrayref
            }

           To undefine/clear this callback use:

            Net::SSleay::CTX_set_next_protos_advertised_cb($ctx, undef);

       o   P_next_proto_negotiated

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-1.0.1

           Returns the name of negotiated protocol for given SSL connection
           $ssl.

            $rv = Net::SSLeay::P_next_proto_negotiated($ssl)
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: (string) negotiated protocol name (or undef if no negotiation was done or failed with fatal error)

       o   P_next_proto_last_status

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before;
           requires at least openssl-1.0.1

           Returns the result of the last negotiation for given SSL connection
           $ssl.

            $rv = Net::SSLeay::P_next_proto_last_status($ssl)
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: (integer) negotiation status
            #          0 - OPENSSL_NPN_UNSUPPORTED
            #          1 - OPENSSL_NPN_NEGOTIATED
            #          2 - OPENSSL_NPN_NO_OVERLAP

       Low level API: ALPN (application layer protocol negotiation) related
       functions

       Application protocol can be negotiated via two different mechanisms
       employing two different TLS extensions: NPN (obsolete) and ALPN
       (recommended).

       The API is rather similar, with slight differences reflecting protocol
       specifics. In particular, with ALPN the protocol negotiation takes
       place on server, while with NPN the client implements the protocol
       negotiation logic.

       With ALPN, the most basic implementation looks like this:

        ### client side
        use Net::SSLeay;
        use IO::Socket::INET;

        Net::SSLeay::initialize();
        my $sock = IO::Socket::INET->new(PeerAddr=>'encrypted.google.com:443') or die;
        my $ctx = Net::SSLeay::CTX_tlsv1_new() or die;
        Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL);
        Net::SSLeay::CTX_set_alpn_protos($ctx, ['http/1.1', 'http/2.0', 'spdy/3]);
        my $ssl = Net::SSLeay::new($ctx) or die;
        Net::SSLeay::set_fd($ssl, fileno($sock)) or die;
        Net::SSLeay::connect($ssl);

        warn "client:selected=",Net::SSLeay::P_alpn_selected($ssl), "\n";

        ### server side
        use Net::SSLeay;
        use IO::Socket::INET;

        Net::SSLeay::initialize();
        my $ctx = Net::SSLeay::CTX_tlsv1_new() or die;
        Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL);
        Net::SSLeay::set_cert_and_key($ctx, "t/data/cert.pem", "t/data/key.pem");
        Net::SSLeay::CTX_set_alpn_select_cb($ctx, ['http/1.1', 'http/2.0', 'spdy/3]);
        my $sock = IO::Socket::INET->new(LocalAddr=>'localhost', LocalPort=>5443, Proto=>'tcp', Listen=>20) or die;

        while (1) {
          my $ssl = Net::SSLeay::new($ctx);
          warn("server:waiting for incoming connection...\n");
          my $fd = $sock->accept();
          Net::SSLeay::set_fd($ssl, $fd->fileno);
          Net::SSLeay::accept($ssl);
          warn "server:selected=",Net::SSLeay::P_alpn_selected($ssl),"\n";
          my $got = Net::SSLeay::read($ssl);
          Net::SSLeay::ssl_write_all($ssl, "length=".length($got));
          Net::SSLeay::free($ssl);
          $fd->close();
        }
        # check with: openssl s_client -connect localhost:5443 -alpn spdy/3,http/1.1

       Advanced approach allows you to implement your own negotiation
       algorithm.

        #see below documentation for:
        Net::SSleay::CTX_set_alpn_select_cb($ctx, $perl_callback_function, $callback_data);

       Detection of ALPN support (works even in older Net::SSLeay versions):

        use Net::SSLeay;

        if (exists &Net::SSLeay::P_alpn_selected) {
          # do ALPN stuff
        }

       o   CTX_set_alpn_select_cb

           COMPATIBILITY: not available in Net-SSLeay-1.55 and before;
           requires at least openssl-1.0.2

           NOTE: You need CTX_set_alpn_select_cb on server side of TLS
           connection.

           Simple usage - in this case a "common" negotiation algorithm (as
           implemented by openssl's function SSL_select_next_proto) is used.

            $rv = Net::SSleay::CTX_set_alpn_select_cb($ctx, $arrayref);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $arrayref - list of accepted protocols - e.g. ['http/2.0', 'http/1.1', 'spdy/3']
            #
            # returns: 0 on success, 1 on failure

           Advanced usage (you probably do not need this):

            $rv = Net::SSleay::CTX_set_alpn_select_cb($ctx, $perl_callback_function, $callback_data);
            # $ctx - value corresponding to openssl's SSL_CTX structure
            # $perl_callback_function - reference to perl function
            # $callback_data - [optional] data to passed to callback function when invoked
            #
            # returns: 0 on success, 1 on failure

            # where callback function looks like
            sub alpn_select_cb_invoke {
              my ($ssl, $arrayref_proto_list_advertised_by_client, $callback_data) = @_;
              # ...
              if ($negotiated) {
                return 'http/2.0';
              } else {
                return undef;
              }
            }

           To undefine/clear this callback use:

            Net::SSleay::CTX_set_alpn_select_cb($ctx, undef);

       o   set_alpn_protos

           COMPATIBILITY: not available in Net-SSLeay-1.55 and before;
           requires at least openssl-1.0.2

           NOTE: You need set_alpn_protos on client side of TLS connection.

           This adds list of supported application layer protocols to
           ClientHello message sent by a client.  It advertises the
           enumeration of supported protocols:

            Net::SSLeay::set_alpn_protos($ssl, ['http/1.1', 'http/2.0', 'spdy/3]);
            # returns 0 on success

       o   CTX_set_alpn_protos

           COMPATIBILITY: not available in Net-SSLeay-1.55 and before;
           requires at least openssl-1.0.2

           NOTE: You need CTX_set_alpn_protos on client side of TLS
           connection.

           This adds list of supported application layer protocols to
           ClientHello message sent by a client.  It advertises the
           enumeration of supported protocols:

            Net::SSLeay::CTX_set_alpn_protos($ctx, ['http/1.1', 'http/2.0', 'spdy/3]);
            # returns 0 on success

       o   P_alpn_selected

           COMPATIBILITY: not available in Net-SSLeay-1.55 and before;
           requires at least openssl-1.0.2

           Returns the name of negotiated protocol for given TLS connection
           $ssl.

            $rv = Net::SSLeay::P_alpn_selected($ssl)
            # $ssl - value corresponding to openssl's SSL structure
            #
            # returns: (string) negotiated protocol name (or undef if no negotiation was done or failed with fatal error)

       Low level API: DANE Support

       OpenSSL version 1.0.2 adds preliminary support RFC6698 Domain
       Authentication of Named Entities (DANE) Transport Layer Association
       within OpenSSL

       o   SSL_get_tlsa_record_byname

           COMPATIBILITY: DELETED from net-ssleay, since it is not supported
           by OpenSSL

           In order to facilitate DANE there is additional interface,
           SSL_get_tlsa_record_byname, accepting hostname, port and socket
           type that returns packed TLSA record. In order to make it even
           easier there is additional SSL_ctrl function that calls
           SSL_get_tlsa_record_byname for you. Latter is recommended for
           programmers that wish to maintain broader binary compatibility,
           e.g. make application work with both 1.0.2 and prior version (in
           which case call to SSL_ctrl with new code returning error would
           have to be ignored when running with prior version).

           Net::SSLeay::get_tlsa_record_byname($name, $port, $type);

       Low level API: Other functions

       o   COMP_add_compression_method

           Adds the compression method cm with the identifier id to the list
           of available compression methods.  This list is globally maintained
           for all SSL operations within this application.  It cannot be set
           for specific SSL_CTX or SSL objects.

            my $rv = Net::SSLeay::COMP_add_compression_method($id, $cm);
            # $id - (integer) compression method id
            #       0 to 63:    methods defined by the IETF
            #       64 to 192:  external party methods assigned by IANA
            #       193 to 255: reserved for private use
            #
            # $cm - value corresponding to openssl's COMP_METHOD structure
            #
            # returns: 0 on success, 1 on failure (check the error queue to find out the reason)

           Check openssl doc
           <http://www.openssl.org/docs/ssl/SSL_COMP_add_compression_method.html>

       o   DH_free

           Frees the DH structure and its components. The values are erased
           before the memory is returned to the system.

            Net::SSLeay::DH_free($dh);
            # $dh - value corresponding to openssl's DH structure
            #
            # returns: no return value

           Check openssl doc <http://www.openssl.org/docs/crypto/DH_new.html>

       o   FIPS_mode_set

           Enable or disable FIPS mode in a FIPS capable OpenSSL.

            Net::SSLeay:: FIPS_mode_set($enable);
            # $enable - (integer) 1 to enable, 0 to disable

       Low level API: EC related functions

       o   CTX_set_tmp_ecdh

           TBA

       o   EC_KEY_free

           TBA

       o   EC_KEY_new_by_curve_name

           TBA

       o   EC_KEY_generate_key

           Generates a EC key and returns it in a newly allocated EC_KEY
           structure.  The EC key then can be used to create a PKEY which can
           be used in calls like X509_set_pubkey.

            my $key = Net::SSLeay::EVP_PKEY_new();
            my $ec  = Net::SSLeay::EC_KEY_generate_key($curve);
            Net::SSLeay::EVP_PKEY_assign_EC_KEY($key,$ec);

            # $curve - curve name like 'secp521r1' or the matching Id (integer) of the curve
            #
            # returns: value corresponding to openssl's EC_KEY structure (0 on failure)

           This function has no equivalent in OpenSSL but combines multiple
           OpenSSL functions for an easier interface.

   Constants
       There are many openssl constants available in Net::SSLeay. You can use
       them like this:

        use Net::SSLeay;
        print &Net::SSLeay::NID_commonName;
        #or
        print Net::SSLeay::NID_commonName();

       Or you can import them and use:

        use Net::SSLeay qw/NID_commonName/;
        print &NID_commonName;
        #or
        print NID_commonName();
        #or
        print NID_commonName;

       The constants names are derived from openssl constants, however
       constants starting with "SSL_" prefix have name with "SSL_" part
       stripped - e.g. openssl's constant "SSL_OP_ALL" is available as
       "Net::SSleay::OP_ALL"

       The list of all available constant names:

        ASN1_STRFLGS_ESC_CTRL           NID_ext_key_usage                      OP_CRYPTOPRO_TLSEXT_BUG
        ASN1_STRFLGS_ESC_MSB            NID_ext_req                            OP_DONT_INSERT_EMPTY_FRAGMENTS
        ASN1_STRFLGS_ESC_QUOTE          NID_friendlyName                       OP_EPHEMERAL_RSA
        ASN1_STRFLGS_RFC2253            NID_givenName                          OP_LEGACY_SERVER_CONNECT
        CB_ACCEPT_EXIT                  NID_hmacWithSHA1                       OP_MICROSOFT_BIG_SSLV3_BUFFER
        CB_ACCEPT_LOOP                  NID_id_ad                              OP_MICROSOFT_SESS_ID_BUG
        CB_ALERT                        NID_id_ce                              OP_MSIE_SSLV2_RSA_PADDING
        CB_CONNECT_EXIT                 NID_id_kp                              OP_NETSCAPE_CA_DN_BUG
        CB_CONNECT_LOOP                 NID_id_pbkdf2                          OP_NETSCAPE_CHALLENGE_BUG
        CB_EXIT                         NID_id_pe                              OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
        CB_HANDSHAKE_DONE               NID_id_pkix                            OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
        CB_HANDSHAKE_START              NID_id_qt_cps                          OP_NON_EXPORT_FIRST
        CB_LOOP                         NID_id_qt_unotice                      OP_NO_COMPRESSION
        CB_READ                         NID_idea_cbc                           OP_NO_QUERY_MTU
        CB_READ_ALERT                   NID_idea_cfb64                         OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
        CB_WRITE                        NID_idea_ecb                           OP_NO_SSLv2
        CB_WRITE_ALERT                  NID_idea_ofb64                         OP_NO_SSLv3
        ERROR_NONE                      NID_info_access                        OP_NO_TICKET
        ERROR_SSL                       NID_initials                           OP_NO_TLSv1
        ERROR_SYSCALL                   NID_invalidity_date                    OP_NO_TLSv1_1
        ERROR_WANT_ACCEPT               NID_issuer_alt_name                    OP_NO_TLSv1_2
        ERROR_WANT_CONNECT              NID_keyBag                             OP_PKCS1_CHECK_1
        ERROR_WANT_READ                 NID_key_usage                          OP_PKCS1_CHECK_2
        ERROR_WANT_WRITE                NID_localKeyID                         OP_SINGLE_DH_USE
        ERROR_WANT_X509_LOOKUP          NID_localityName                       OP_SINGLE_ECDH_USE
        ERROR_ZERO_RETURN               NID_md2                                OP_SSLEAY_080_CLIENT_DH_BUG
        EVP_PKS_DSA                     NID_md2WithRSAEncryption               OP_SSLREF2_REUSE_CERT_TYPE_BUG
        EVP_PKS_EC                      NID_md5                                OP_TLS_BLOCK_PADDING_BUG
        EVP_PKS_RSA                     NID_md5WithRSA                         OP_TLS_D5_BUG
        EVP_PKT_ENC                     NID_md5WithRSAEncryption               OP_TLS_ROLLBACK_BUG
        EVP_PKT_EXCH                    NID_md5_sha1                           READING
        EVP_PKT_EXP                     NID_mdc2                               RECEIVED_SHUTDOWN
        EVP_PKT_SIGN                    NID_mdc2WithRSA                        RSA_3
        EVP_PK_DH                       NID_ms_code_com                        RSA_F4
        EVP_PK_DSA                      NID_ms_code_ind                        R_BAD_AUTHENTICATION_TYPE
        EVP_PK_EC                       NID_ms_ctl_sign                        R_BAD_CHECKSUM
        EVP_PK_RSA                      NID_ms_efs                             R_BAD_MAC_DECODE
        FILETYPE_ASN1                   NID_ms_ext_req                         R_BAD_RESPONSE_ARGUMENT
        FILETYPE_PEM                    NID_ms_sgc                             R_BAD_SSL_FILETYPE
        F_CLIENT_CERTIFICATE            NID_name                               R_BAD_SSL_SESSION_ID_LENGTH
        F_CLIENT_HELLO                  NID_netscape                           R_BAD_STATE
        F_CLIENT_MASTER_KEY             NID_netscape_base_url                  R_BAD_WRITE_RETRY
        F_D2I_SSL_SESSION               NID_netscape_ca_policy_url             R_CHALLENGE_IS_DIFFERENT
        F_GET_CLIENT_FINISHED           NID_netscape_ca_revocation_url         R_CIPHER_TABLE_SRC_ERROR
        F_GET_CLIENT_HELLO              NID_netscape_cert_extension            R_INVALID_CHALLENGE_LENGTH
        F_GET_CLIENT_MASTER_KEY         NID_netscape_cert_sequence             R_NO_CERTIFICATE_SET
        F_GET_SERVER_FINISHED           NID_netscape_cert_type                 R_NO_CERTIFICATE_SPECIFIED
        F_GET_SERVER_HELLO              NID_netscape_comment                   R_NO_CIPHER_LIST
        F_GET_SERVER_VERIFY             NID_netscape_data_type                 R_NO_CIPHER_MATCH
        F_I2D_SSL_SESSION               NID_netscape_renewal_url               R_NO_PRIVATEKEY
        F_READ_N                        NID_netscape_revocation_url            R_NO_PUBLICKEY
        F_REQUEST_CERTIFICATE           NID_netscape_ssl_server_name           R_NULL_SSL_CTX
        F_SERVER_HELLO                  NID_ns_sgc                             R_PEER_DID_NOT_RETURN_A_CERTIFICATE
        F_SSL_CERT_NEW                  NID_organizationName                   R_PEER_ERROR
        F_SSL_GET_NEW_SESSION           NID_organizationalUnitName             R_PEER_ERROR_CERTIFICATE
        F_SSL_NEW                       NID_pbeWithMD2AndDES_CBC               R_PEER_ERROR_NO_CIPHER
        F_SSL_READ                      NID_pbeWithMD2AndRC2_CBC               R_PEER_ERROR_UNSUPPORTED_CERTIFICATE_TYPE
        F_SSL_RSA_PRIVATE_DECRYPT       NID_pbeWithMD5AndCast5_CBC             R_PUBLIC_KEY_ENCRYPT_ERROR
        F_SSL_RSA_PUBLIC_ENCRYPT        NID_pbeWithMD5AndDES_CBC               R_PUBLIC_KEY_IS_NOT_RSA
        F_SSL_SESSION_NEW               NID_pbeWithMD5AndRC2_CBC               R_READ_WRONG_PACKET_TYPE
        F_SSL_SESSION_PRINT_FP          NID_pbeWithSHA1AndDES_CBC              R_SHORT_READ
        F_SSL_SET_FD                    NID_pbeWithSHA1AndRC2_CBC              R_SSL_SESSION_ID_IS_DIFFERENT
        F_SSL_SET_RFD                   NID_pbe_WithSHA1And128BitRC2_CBC       R_UNABLE_TO_EXTRACT_PUBLIC_KEY
        F_SSL_SET_WFD                   NID_pbe_WithSHA1And128BitRC4           R_UNKNOWN_REMOTE_ERROR_TYPE
        F_SSL_USE_CERTIFICATE           NID_pbe_WithSHA1And2_Key_TripleDES_CBC R_UNKNOWN_STATE
        F_SSL_USE_CERTIFICATE_ASN1      NID_pbe_WithSHA1And3_Key_TripleDES_CBC R_X509_LIB
        F_SSL_USE_CERTIFICATE_FILE      NID_pbe_WithSHA1And40BitRC2_CBC        SENT_SHUTDOWN
        F_SSL_USE_PRIVATEKEY            NID_pbe_WithSHA1And40BitRC4            SESSION_ASN1_VERSION
        F_SSL_USE_PRIVATEKEY_ASN1       NID_pbes2                              ST_ACCEPT
        F_SSL_USE_PRIVATEKEY_FILE       NID_pbmac1                             ST_BEFORE
        F_SSL_USE_RSAPRIVATEKEY         NID_pkcs                               ST_CONNECT
        F_SSL_USE_RSAPRIVATEKEY_ASN1    NID_pkcs3                              ST_INIT
        F_SSL_USE_RSAPRIVATEKEY_FILE    NID_pkcs7                              ST_OK
        F_WRITE_PENDING                 NID_pkcs7_data                         ST_READ_BODY
        GEN_DIRNAME                     NID_pkcs7_digest                       ST_READ_HEADER
        GEN_DNS                         NID_pkcs7_encrypted                    TLSEXT_STATUSTYPE_ocsp
        GEN_EDIPARTY                    NID_pkcs7_enveloped                    VERIFY_CLIENT_ONCE
        GEN_EMAIL                       NID_pkcs7_signed                       VERIFY_FAIL_IF_NO_PEER_CERT
        GEN_IPADD                       NID_pkcs7_signedAndEnveloped           VERIFY_NONE
        GEN_OTHERNAME                   NID_pkcs8ShroudedKeyBag                VERIFY_PEER
        GEN_RID                         NID_pkcs9                              V_OCSP_CERTSTATUS_GOOD
        GEN_URI                         NID_pkcs9_challengePassword            V_OCSP_CERTSTATUS_REVOKED
        GEN_X400                        NID_pkcs9_contentType                  V_OCSP_CERTSTATUS_UNKNOWN
        LIBRESSL_VERSION_NUMBER         NID_pkcs9_countersignature             WRITING
        MBSTRING_ASC                    NID_pkcs9_emailAddress                 X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT
        MBSTRING_BMP                    NID_pkcs9_extCertAttributes            X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS
        MBSTRING_FLAG                   NID_pkcs9_messageDigest                X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS
        MBSTRING_UNIV                   NID_pkcs9_signingTime                  X509_CHECK_FLAG_NO_WILDCARDS
        MBSTRING_UTF8                   NID_pkcs9_unstructuredAddress          X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS
        MIN_RSA_MODULUS_LENGTH_IN_BYTES NID_pkcs9_unstructuredName             X509_LOOKUP
        MODE_ACCEPT_MOVING_WRITE_BUFFER NID_private_key_usage_period           X509_PURPOSE_ANY
        MODE_AUTO_RETRY                 NID_rc2_40_cbc                         X509_PURPOSE_CRL_SIGN
        MODE_ENABLE_PARTIAL_WRITE       NID_rc2_64_cbc                         X509_PURPOSE_NS_SSL_SERVER
        MODE_RELEASE_BUFFERS            NID_rc2_cbc                            X509_PURPOSE_OCSP_HELPER
        NID_OCSP_sign                   NID_rc2_cfb64                          X509_PURPOSE_SMIME_ENCRYPT
        NID_SMIMECapabilities           NID_rc2_ecb                            X509_PURPOSE_SMIME_SIGN
        NID_X500                        NID_rc2_ofb64                          X509_PURPOSE_SSL_CLIENT
        NID_X509                        NID_rc4                                X509_PURPOSE_SSL_SERVER
        NID_ad_OCSP                     NID_rc4_40                             X509_PURPOSE_TIMESTAMP_SIGN
        NID_ad_ca_issuers               NID_rc5_cbc                            X509_TRUST_COMPAT
        NID_algorithm                   NID_rc5_cfb64                          X509_TRUST_EMAIL
        NID_authority_key_identifier    NID_rc5_ecb                            X509_TRUST_OBJECT_SIGN
        NID_basic_constraints           NID_rc5_ofb64                          X509_TRUST_OCSP_REQUEST
        NID_bf_cbc                      NID_ripemd160                          X509_TRUST_OCSP_SIGN
        NID_bf_cfb64                    NID_ripemd160WithRSA                   X509_TRUST_SSL_CLIENT
        NID_bf_ecb                      NID_rle_compression                    X509_TRUST_SSL_SERVER
        NID_bf_ofb64                    NID_rsa                                X509_TRUST_TSA
        NID_cast5_cbc                   NID_rsaEncryption                      X509_V_FLAG_ALLOW_PROXY_CERTS
        NID_cast5_cfb64                 NID_rsadsi                             X509_V_FLAG_CB_ISSUER_CHECK
        NID_cast5_ecb                   NID_safeContentsBag                    X509_V_FLAG_CHECK_SS_SIGNATURE
        NID_cast5_ofb64                 NID_sdsiCertificate                    X509_V_FLAG_CRL_CHECK
        NID_certBag                     NID_secretBag                          X509_V_FLAG_CRL_CHECK_ALL
        NID_certificate_policies        NID_serialNumber                       X509_V_FLAG_EXPLICIT_POLICY
        NID_client_auth                 NID_server_auth                        X509_V_FLAG_EXTENDED_CRL_SUPPORT
        NID_code_sign                   NID_sha                                X509_V_FLAG_IGNORE_CRITICAL
        NID_commonName                  NID_sha1                               X509_V_FLAG_INHIBIT_ANY
        NID_countryName                 NID_sha1WithRSA                        X509_V_FLAG_INHIBIT_MAP
        NID_crlBag                      NID_sha1WithRSAEncryption              X509_V_FLAG_NOTIFY_POLICY
        NID_crl_distribution_points     NID_shaWithRSAEncryption               X509_V_FLAG_POLICY_CHECK
        NID_crl_number                  NID_stateOrProvinceName                X509_V_FLAG_POLICY_MASK
        NID_crl_reason                  NID_subject_alt_name                   X509_V_FLAG_TRUSTED_FIRST
        NID_delta_crl                   NID_subject_key_identifier             X509_V_FLAG_USE_CHECK_TIME
        NID_des_cbc                     NID_surname                            X509_V_FLAG_USE_DELTAS
        NID_des_cfb64                   NID_sxnet                              X509_V_FLAG_X509_STRICT
        NID_des_ecb                     NID_time_stamp                         X509_V_OK
        NID_des_ede                     NID_title                              XN_FLAG_COMPAT
        NID_des_ede3                    NID_undef                              XN_FLAG_DN_REV
        NID_des_ede3_cbc                NID_uniqueIdentifier                   XN_FLAG_DUMP_UNKNOWN_FIELDS
        NID_des_ede3_cfb64              NID_x509Certificate                    XN_FLAG_FN_ALIGN
        NID_des_ede3_ofb64              NID_x509Crl                            XN_FLAG_FN_LN
        NID_des_ede_cbc                 NID_zlib_compression                   XN_FLAG_FN_MASK
        NID_des_ede_cfb64               NOTHING                                XN_FLAG_FN_NONE
        NID_des_ede_ofb64               OCSP_RESPONSE_STATUS_INTERNALERROR     XN_FLAG_FN_OID
        NID_des_ofb64                   OCSP_RESPONSE_STATUS_MALFORMEDREQUEST  XN_FLAG_FN_SN
        NID_description                 OCSP_RESPONSE_STATUS_SIGREQUIRED       XN_FLAG_MULTILINE
        NID_desx_cbc                    OCSP_RESPONSE_STATUS_SUCCESSFUL        XN_FLAG_ONELINE
        NID_dhKeyAgreement              OCSP_RESPONSE_STATUS_TRYLATER          XN_FLAG_RFC2253
        NID_dnQualifier                 OCSP_RESPONSE_STATUS_UNAUTHORIZED      XN_FLAG_SEP_COMMA_PLUS
        NID_dsa                         OPENSSL_VERSION_NUMBER                 XN_FLAG_SEP_CPLUS_SPC
        NID_dsaWithSHA                  OP_ALL                                 XN_FLAG_SEP_MASK
        NID_dsaWithSHA1                 OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION   XN_FLAG_SEP_MULTILINE
        NID_dsaWithSHA1_2               OP_CIPHER_SERVER_PREFERENCE            XN_FLAG_SEP_SPLUS_SPC
        NID_dsa_2                       OP_CISCO_ANYCONNECT                    XN_FLAG_SPC_EQ
        NID_email_protect               OP_COOKIE_EXCHANGE
       =head2 INTERNAL ONLY functions (do not use these)

       The following functions are not intended for use from outside of
       Net::SSLeay module.  They might be removed, renamed or changed without
       prior notice in future version.

       Simply DO NOT USE THEM!

       o   hello

       o   blength

       o   constant


EXAMPLES

       One very good example to look at is the implementation of "sslcat()" in
       the "SSLeay.pm" file.

       The following is a simple SSLeay client (with too little error checking
       :-(

           #!/usr/bin/perl
           use Socket;
           use Net::SSLeay qw(die_now die_if_ssl_error) ;
           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

           ($dest_serv, $port, $msg) = @ARGV;      # Read command line
           $port = getservbyname ($port, 'tcp') unless $port =~ /^\d+$/;
           $dest_ip = gethostbyname ($dest_serv);
           $dest_serv_params  = sockaddr_in($port, $dest_ip);

           socket  (S, &AF_INET, &SOCK_STREAM, 0)  or die "socket: $!";
           connect (S, $dest_serv_params)          or die "connect: $!";
           select  (S); $| = 1; select (STDOUT);   # Eliminate STDIO buffering

           # The network connection is now open, lets fire up SSL

           $ctx = Net::SSLeay::CTX_new() or die_now("Failed to create SSL_CTX $!");
           Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL)
                or die_if_ssl_error("ssl ctx set options");
           $ssl = Net::SSLeay::new($ctx) or die_now("Failed to create SSL $!");
           Net::SSLeay::set_fd($ssl, fileno(S));   # Must use fileno
           $res = Net::SSLeay::connect($ssl) and die_if_ssl_error("ssl connect");
           print "Cipher `" . Net::SSLeay::get_cipher($ssl) . "'\n";

           # Exchange data

           $res = Net::SSLeay::write($ssl, $msg);  # Perl knows how long $msg is
           die_if_ssl_error("ssl write");
           CORE::shutdown S, 1;  # Half close --> No more output, sends EOF to server
           $got = Net::SSLeay::read($ssl);         # Perl returns undef on failure
           die_if_ssl_error("ssl read");
           print $got;

           Net::SSLeay::free ($ssl);               # Tear down connection
           Net::SSLeay::CTX_free ($ctx);
           close S;

       The following is a simple SSLeay echo server (non forking):

           #!/usr/bin/perl -w
           use Socket;
           use Net::SSLeay qw(die_now die_if_ssl_error);
           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

           $our_ip = "\0\0\0\0"; # Bind to all interfaces
           $port = 1235;
           $sockaddr_template = 'S n a4 x8';
           $our_serv_params = pack ($sockaddr_template, &AF_INET, $port, $our_ip);

           socket (S, &AF_INET, &SOCK_STREAM, 0)  or die "socket: $!";
           bind (S, $our_serv_params)             or die "bind:   $!";
           listen (S, 5)                          or die "listen: $!";
           $ctx = Net::SSLeay::CTX_new ()         or die_now("CTX_new ($ctx): $!");
           Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL)
                or die_if_ssl_error("ssl ctx set options");

           # Following will ask password unless private key is not encrypted
           Net::SSLeay::CTX_use_RSAPrivateKey_file ($ctx, 'plain-rsa.pem',
                                                    &Net::SSLeay::FILETYPE_PEM);
           die_if_ssl_error("private key");
           Net::SSLeay::CTX_use_certificate_file ($ctx, 'plain-cert.pem',
                                                  &Net::SSLeay::FILETYPE_PEM);
           die_if_ssl_error("certificate");

           while (1) {
               print "Accepting connections...\n";
               ($addr = accept (NS, S))           or die "accept: $!";
               select (NS); $| = 1; select (STDOUT);  # Piping hot!

               ($af,$client_port,$client_ip) = unpack($sockaddr_template,$addr);
               @inetaddr = unpack('C4',$client_ip);
               print "$af connection from " .
               join ('.', @inetaddr) . ":$client_port\n";

               # We now have a network connection, lets fire up SSLeay...

               $ssl = Net::SSLeay::new($ctx)      or die_now("SSL_new ($ssl): $!");
               Net::SSLeay::set_fd($ssl, fileno(NS));

               $err = Net::SSLeay::accept($ssl) and die_if_ssl_error('ssl accept');
               print "Cipher `" . Net::SSLeay::get_cipher($ssl) . "'\n";

               # Connected. Exchange some data.

               $got = Net::SSLeay::read($ssl);     # Returns undef on fail
               die_if_ssl_error("ssl read");
               print "Got `$got' (" . length ($got) . " chars)\n";

               Net::SSLeay::write ($ssl, uc ($got)) or die "write: $!";
               die_if_ssl_error("ssl write");

               Net::SSLeay::free ($ssl);           # Tear down connection
               close NS;
           }

       Yet another echo server. This one runs from "/etc/inetd.conf" so it
       avoids all the socket code overhead. Only caveat is opening an rsa key
       file - it had better be without any encryption or else it will not know
       where to ask for the password. Note how "STDIN" and "STDOUT" are wired
       to SSL.

           #!/usr/bin/perl
           # /etc/inetd.conf
           #    ssltst stream tcp nowait root /path/to/server.pl server.pl
           # /etc/services
           #    ssltst         1234/tcp

           use Net::SSLeay qw(die_now die_if_ssl_error);
           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

           chdir '/key/dir' or die "chdir: $!";
           $| = 1;  # Piping hot!
           open LOG, ">>/dev/console" or die "Can't open log file $!";
           select LOG; print "server.pl started\n";

           $ctx = Net::SSLeay::CTX_new()     or die_now "CTX_new ($ctx) ($!)";
           $ssl = Net::SSLeay::new($ctx)     or die_now "new ($ssl) ($!)";
           Net::SSLeay::set_options($ssl, &Net::SSLeay::OP_ALL)
                and die_if_ssl_error("ssl set options");

           # We get already open network connection from inetd, now we just
           # need to attach SSLeay to STDIN and STDOUT
           Net::SSLeay::set_rfd($ssl, fileno(STDIN));
           Net::SSLeay::set_wfd($ssl, fileno(STDOUT));

           Net::SSLeay::use_RSAPrivateKey_file ($ssl, 'plain-rsa.pem',
                                                Net::SSLeay::FILETYPE_PEM);
           die_if_ssl_error("private key");
           Net::SSLeay::use_certificate_file ($ssl, 'plain-cert.pem',
                                              Net::SSLeay::FILETYPE_PEM);
           die_if_ssl_error("certificate");

           Net::SSLeay::accept($ssl) and die_if_ssl_err("ssl accept: $!");
           print "Cipher `" . Net::SSLeay::get_cipher($ssl) . "'\n";

           $got = Net::SSLeay::read($ssl);
           die_if_ssl_error("ssl read");
           print "Got `$got' (" . length ($got) . " chars)\n";

           Net::SSLeay::write ($ssl, uc($got)) or die "write: $!";
           die_if_ssl_error("ssl write");

           Net::SSLeay::free ($ssl);         # Tear down the connection
           Net::SSLeay::CTX_free ($ctx);
           close LOG;

       There are also a number of example/test programs in the examples
       directory:

           sslecho.pl   -  A simple server, not unlike the one above
           minicli.pl   -  Implements a client using low level SSLeay routines
           sslcat.pl    -  Demonstrates using high level sslcat utility function
           get_page.pl  -  Is a utility for getting html pages from secure servers
           callback.pl  -  Demonstrates certificate verification and callback usage
           stdio_bulk.pl       - Does SSL over Unix pipes
           ssl-inetd-serv.pl   - SSL server that can be invoked from inetd.conf
           httpd-proxy-snif.pl - Utility that allows you to see how a browser
                                 sends https request to given server and what reply
                                 it gets back (very educative :-)
           makecert.pl  -  Creates a self signed cert (does not use this module)


INSTALLATION

       See README and README.* in the distribution directory for installation
       guidance on a variety of platforms.


LIMITATIONS

       "Net::SSLeay::read()" uses an internal buffer of 32KB, thus no single
       read will return more. In practice one read returns much less, usually
       as much as fits in one network packet. To work around this, you should
       use a loop like this:

           $reply = '';
           while ($got = Net::SSLeay::read($ssl)) {
               last if print_errs('SSL_read');
               $reply .= $got;
           }

       Although there is no built-in limit in "Net::SSLeay::write()", the
       network packet size limitation applies here as well, thus use:

           $written = 0;

           while ($written < length($message)) {
               $written += Net::SSLeay::write($ssl, substr($message, $written));
               last if print_errs('SSL_write');
           }

       Or alternatively you can just use the following convenience functions:

           Net::SSLeay::ssl_write_all($ssl, $message) or die "ssl write failure";
           $got = Net::SSLeay::ssl_read_all($ssl) or die "ssl read failure";


KNOWN BUGS AND CAVEATS

       An OpenSSL bug CVE-2015-0290 "OpenSSL Multiblock Corrupted Pointer
       Issue" can cause POST requests of over 90kB to fail or crash. This bug
       is reported to be fixed in OpenSSL 1.0.2a.

       Autoloader emits a

           Argument "xxx" isn't numeric in entersub at blib/lib/Net/SSLeay.pm'

       warning if die_if_ssl_error is made autoloadable. If you figure out
       why, drop me a line.

       Callback set using "SSL_set_verify()" does not appear to work. This may
       well be an openssl problem (e.g. see "ssl/ssl_lib.c" line 1029). Try
       using "SSL_CTX_set_verify()" instead and do not be surprised if even
       this stops working in future versions.

       Callback and certificate verification stuff is generally too little
       tested.

       Random numbers are not initialized randomly enough, especially if you
       do not have "/dev/random" and/or "/dev/urandom" (such as in Solaris
       platforms - but it's been suggested that cryptorand daemon from the
       SUNski package solves this). In this case you should investigate third
       party software that can emulate these devices, e.g. by way of a named
       pipe to some program.

       Another gotcha with random number initialization is randomness
       depletion. This phenomenon, which has been extensively discussed in
       OpenSSL, Apache-SSL, and Apache-mod_ssl forums, can cause your script
       to block if you use "/dev/random" or to operate insecurely if you use
       "/dev/urandom". What happens is that when too much randomness is drawn
       from the operating system's randomness pool then randomness can
       temporarily be unavailable. "/dev/random" solves this problem by
       waiting until enough randomness can be gathered - and this can take a
       long time since blocking reduces activity in the machine and less
       activity provides less random events: a vicious circle.  "/dev/urandom"
       solves this dilemma more pragmatically by simply returning predictable
       "random" numbers. Some" /dev/urandom" emulation software however
       actually seems to implement "/dev/random" semantics. Caveat emptor.

       I've been pointed to two such daemons by Mik Firestone
       <mik@@speed.stdio._com> who has used them on Solaris 8:

       1.  Entropy Gathering Daemon (EGD) at
           <http://www.lothar.com/tech/crypto/>

       2.  Pseudo-random number generating daemon (PRNGD) at
           <http://www.aet.tu-cottbus.de/personen/jaenicke/postfix_tls/prngd.html>

       If you are using the low level API functions to communicate with other
       SSL implementations, you would do well to call

           Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL)
                or die_if_ssl_error("ssl ctx set options");

       to cope with some well know bugs in some other SSL implementations. The
       high level API functions always set all known compatibility options.

       Sometimes "sslcat()" (and the high level HTTPS functions that build on
       it) is too fast in signaling the EOF to legacy HTTPS servers. This
       causes the server to return empty page. To work around this problem you
       can set the global variable

           $Net::SSLeay::slowly = 1;   # Add sleep so broken servers can keep up

       HTTP/1.1 is not supported. Specifically this module does not know to
       issue or serve multiple http requests per connection. This is a serious
       shortcoming, but using the SSL session cache on your server helps to
       alleviate the CPU load somewhat.

       As of version 1.09 many newer OpenSSL auxiliary functions were added
       (from "REM_AUTOMATICALLY_GENERATED_1_09" onwards in "SSLeay.xs").
       Unfortunately I have not had any opportunity to test these. Some of
       them are trivial enough that I believe they "just work", but others
       have rather complex interfaces with function pointers and all. In these
       cases you should proceed wit great caution.

       This module defaults to using OpenSSL automatic protocol negotiation
       code for automatically detecting the version of the SSL protocol that
       the other end talks. With most web servers this works just fine, but
       once in a while I get complaints from people that the module does not
       work with some web servers. Usually this can be solved by explicitly
       setting the protocol version, e.g.

          $Net::SSLeay::ssl_version = 2;  # Insist on SSLv2
          $Net::SSLeay::ssl_version = 3;  # Insist on SSLv3
          $Net::SSLeay::ssl_version = 10; # Insist on TLSv1

       Although the autonegotiation is nice to have, the SSL standards do not
       formally specify any such mechanism. Most of the world has accepted the
       SSLeay/OpenSSL way of doing it as the de facto standard. But for the
       few that think differently, you have to explicitly speak the correct
       version. This is not really a bug, but rather a deficiency in the
       standards. If a site refuses to respond or sends back some nonsensical
       error codes (at the SSL handshake level), try this option before
       mailing me.

       On some systems, OpenSSL may be compiled without support for SSLv2.  If
       this is the case, Net::SSLeay will warn if ssl_version has been set to
       2.

       The high level API returns the certificate of the peer, thus allowing
       one to check what certificate was supplied. However, you will only be
       able to check the certificate after the fact, i.e. you already sent
       your form data by the time you find out that you did not trust them,
       oops.

       So, while being able to know the certificate after the fact is surely
       useful, the security minded would still choose to do the connection and
       certificate verification first and only then exchange data with the
       site. Currently none of the high level API functions do this, thus you
       would have to program it using the low level API. A good place to start
       is to see how the "Net::SSLeay::http_cat()" function is implemented.

       The high level API functions use a global file handle "SSLCAT_S"
       internally. This really should not be a problem because there is no way
       to interleave the high level API functions, unless you use threads (but
       threads are not very well supported in perl anyway (as of version
       5.6.1). However, you may run into problems if you call undocumented
       internal functions in an interleaved fashion. The best solution is to
       "require Net::SSLeay" in one thread after all the threads have been
       created.


DIAGNOSTICS

       Random number generator not seeded!!!
           (W) This warning indicates that "randomize()" was not able to read
           "/dev/random" or "/dev/urandom", possibly because your system does
           not have them or they are differently named. You can still use SSL,
           but the encryption will not be as strong.

       open_tcp_connection: destination host not found:`server' (port 123)
       ($!)
           Name lookup for host named "server" failed.

       open_tcp_connection: failed `server', 123 ($!)
           The name was resolved, but establishing the TCP connection failed.

       msg 123: 1 - error:140770F8:SSL routines:SSL23_GET_SERVER_HELLO:unknown
       proto
           SSLeay error string. The first number (123) is the PID, the second
           number (1) indicates the position of the error message in SSLeay
           error stack.  You often see a pile of these messages as errors
           cascade.

       msg 123: 1 - error:02001002::lib(2) :func(1) :reason(2)
           The same as above, but you didn't call load_error_strings() so
           SSLeay couldn't verbosely explain the error. You can still find out
           what it means with this command:

               /usr/local/ssl/bin/ssleay errstr 02001002

       Password is being asked for private key
           This is normal behaviour if your private key is encrypted. Either
           you have to supply the password or you have to use an unencrypted
           private key. Scan OpenSSL.org for the FAQ that explains how to do
           this (or just study examples/makecert.pl which is used during "make
           test" to do just that).


SECURITY

       You can mitigate some of the security vulnerabilities that might be
       present in your SSL/TLS application:

   BEAST Attack
       http://blogs.cisco.com/security/beat-the-beast-with-tls/
       https://community.qualys.com/blogs/securitylabs/2011/10/17/mitigating-the-beast-attack-on-tls
       http://blog.zoller.lu/2011/09/beast-summary-tls-cbc-countermeasures.html

       The BEAST attack relies on a weakness in the way CBC mode is used in
       SSL/TLS.  In OpenSSL versions 0.9.6d and later, the protocol-level
       mitigation is enabled by default, thus making it not vulnerable to the
       BEAST attack.

       Solutions:

       o   Compile with OpenSSL versions 0.9.6d or later, which enables
           SSL_OP_ALL by default

       o   Ensure SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS is not enabled (its not
           enabled by default)

       o   Don't support SSLv2, SSLv3

       o   Actively control the ciphers your server supports with
           set_cipher_list:

       Net::SSLeay::set_cipher_list($ssl, 'RC4-SHA:HIGH:!ADH');

   Session Resumption
       http://www.openssl.org/docs/ssl/SSL_CTX_set_options.html

       The SSL Labs vulnerability test on your SSL server might report in red:

       Session resumption      No (IDs assigned but not accepted)

       This report is not really bug or a vulnerability, since the server will
       not accept session resumption requests.  However, you can prevent this
       noise in the report by disabling the session cache altogether:
       Net::SSLeay::CTX_set_session_cache_mode($ssl_ctx, 0);

   Secure Renegotiation and DoS Attack
       https://community.qualys.com/blogs/securitylabs/2011/10/31/tls-renegotiation-and-denial-of-service-attacks

       This is not a "security flaw," it is more of a DoS vulnerability.

       Solutions:

       o   Do not support SSLv2

       o   Do not set the SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION option

       o   Compile with OpenSSL 0.9.8m or later


BUGS AND SUPPORT

       Please report any bugs or feature requests to "bug-Net-SSLeay at
       rt.cpan.org", or through the web interface at
       <http://rt.cpan.org/Public/Dist/Display.html?Name=Net-SSLeay>.  I will
       be notified, and then you'll automatically be notified of progress on
       your bug as I make changes.

       Subversion access to the latest source code etc can be obtained at
       <http://alioth.debian.org/projects/net-ssleay>

       The developer mailing list (for people interested in contributing to
       the source code) can be found at
       <http://lists.alioth.debian.org/mailman/listinfo/net-ssleay-devel>

       You can find documentation for this module with the "perldoc" command.

           perldoc Net::SSLeay

       You can also look for information at:

       o   AnnoCPAN: Annotated CPAN documentation

           <http://annocpan.org/dist/Net-SSLeay>

       o   CPAN Ratings

           <http://cpanratings.perl.org/d/Net-SSLeay>

       o   Search CPAN

           <http://search.cpan.org/dist/Net-SSLeay>

       Commercial support for Net::SSLeay may be obtained from

          Symlabs (netssleay@symlabs.com)
          Tel: +351-214.222.630
          Fax: +351-214.222.637


AUTHOR

       Maintained by Mike McCauley and Florian Ragwitz since November 2005

       Originally written by Sampo KellomAxki <sampo@symlabs.com>


COPYRIGHT

       Copyright (c) 1996-2003 Sampo KellomAxki <sampo@symlabs.com>

       Copyright (C) 2005-2006 Florian Ragwitz <rafl@debian.org>

       Copyright (C) 2005 Mike McCauley <mikem@airspayce.com>

       All Rights Reserved.

       Distribution and use of this module is under the same terms as the
       OpenSSL package itself (i.e. free, but mandatory attribution; NO
       WARRANTY). Please consult LICENSE file in the root of the Net-SSLeay
       distribution, and also included in this distribution.

       The Authors credit Eric Young and the OpenSSL team with the development
       of the excellent OpenSSL library, which this Perl package uses.

       And remember, you, and nobody else but you, are responsible for
       auditing this module and OpenSSL library for security problems,
       backdoors, and general suitability for your application.


LICENSE

       From version 1.66 onwards, this Net-SSLeay library is issued under the
       "Perl Artistic License 2.0", the same license as Perl itself.

       (ignore this line: this is to keep kwalitee happy by saying: Not GPL)


SEE ALSO

         Net::SSLeay::Handle(3)                   - File handle interface
         ./examples                               - Example servers and a clients
         <http://www.openssl.org/>                - OpenSSL source, documentation, etc
         openssl-users-request@openssl.org        - General OpenSSL mailing list
         <http://www.ietf.org/rfc/rfc2246.txt>    - TLS 1.0 specification
         <http://www.w3c.org>                     - HTTP specifications
         <http://www.ietf.org/rfc/rfc2617.txt>    - How to send password
         <http://www.lothar.com/tech/crypto/>     - Entropy Gathering Daemon (EGD)
         <http://www.aet.tu-cottbus.de/personen/jaenicke/postfix_tls/prngd.html>
                                  - pseudo-random number generating daemon (PRNGD)
         perl(1)
         perlref(1)
         perllol(1)
         perldoc ~openssl/doc/ssl/SSL_CTX_set_verify.pod



perl v5.24.2                      2017-10-13                    Net::SSLeay(3)

net-ssleay 1.820.0 - Generated Wed Nov 1 15:52:27 CDT 2017
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