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Digest::SHA(3pm)       Perl Programmers Reference Guide       Digest::SHA(3pm)




NAME

       Digest::SHA - Perl extension for SHA-1/224/256/384/512


SYNOPSIS

       In programs:

                       # Functional interface

               use Digest::SHA qw(sha1 sha1_hex sha1_base64 ...);

               $digest = sha1($data);
               $digest = sha1_hex($data);
               $digest = sha1_base64($data);

               $digest = sha256($data);
               $digest = sha384_hex($data);
               $digest = sha512_base64($data);

                       # Object-oriented

               use Digest::SHA;

               $sha = Digest::SHA->new($alg);

               $sha->add($data);               # feed data into stream

               $sha->addfile(*F);
               $sha->addfile($filename);

               $sha->add_bits($bits);
               $sha->add_bits($data, $nbits);

               $sha_copy = $sha->clone;        # make copy of digest object
               $state = $sha->getstate;        # save current state to string
               $sha->putstate($state);         # restore previous $state

               $digest = $sha->digest;         # compute digest
               $digest = $sha->hexdigest;
               $digest = $sha->b64digest;

       From the command line:

               $ shasum files

               $ shasum --help


SYNOPSIS (HMAC-SHA)

                       # Functional interface only

               use Digest::SHA qw(hmac_sha1 hmac_sha1_hex ...);

               $digest = hmac_sha1($data, $key);
               $digest = hmac_sha224_hex($data, $key);
               $digest = hmac_sha256_base64($data, $key);


ABSTRACT

       Digest::SHA is a complete implementation of the NIST Secure Hash
       Standard.  It gives Perl programmers a convenient way to calculate
       SHA-1, SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, and SHA-512/256
       message digests.  The module can handle all types of input, including
       partial-byte data.


DESCRIPTION

       Digest::SHA is written in C for speed.  If your platform lacks a C
       compiler, you can install the functionally equivalent (but much slower)
       Digest::SHA::PurePerl module.

       The programming interface is easy to use: it's the same one found in
       CPAN's Digest module.  So, if your applications currently use
       Digest::MD5 and you'd prefer the stronger security of SHA, it's a
       simple matter to convert them.

       The interface provides two ways to calculate digests:  all-at-once, or
       in stages.  To illustrate, the following short program computes the
       SHA-256 digest of "hello world" using each approach:

               use Digest::SHA qw(sha256_hex);

               $data = "hello world";
               @frags = split(//, $data);

               # all-at-once (Functional style)
               $digest1 = sha256_hex($data);

               # in-stages (OOP style)
               $state = Digest::SHA->new(256);
               for (@frags) { $state->add($_) }
               $digest2 = $state->hexdigest;

               print $digest1 eq $digest2 ?
                       "whew!\n" : "oops!\n";

       To calculate the digest of an n-bit message where n is not a multiple
       of 8, use the add_bits() method.  For example, consider the 446-bit
       message consisting of the bit-string "110" repeated 148 times, followed
       by "11".  Here's how to display its SHA-1 digest:

               use Digest::SHA;
               $bits = "110" x 148 . "11";
               $sha = Digest::SHA->new(1)->add_bits($bits);
               print $sha->hexdigest, "\n";

       Note that for larger bit-strings, it's more efficient to use the two-
       argument version add_bits($data, $nbits), where $data is in the
       customary packed binary format used for Perl strings.

       The module also lets you save intermediate SHA states to a string.  The
       getstate() method generates portable, human-readable text describing
       the current state of computation.  You can subsequently restore that
       state with putstate() to resume where the calculation left off.

       To see what a state description looks like, just run the following:

               use Digest::SHA;
               print Digest::SHA->new->add("Shaw" x 1962)->getstate;

       As an added convenience, the Digest::SHA module offers routines to
       calculate keyed hashes using the HMAC-SHA-1/224/256/384/512 algorithms.
       These services exist in functional form only, and mimic the style and
       behavior of the sha(), sha_hex(), and sha_base64() functions.

               # Test vector from draft-ietf-ipsec-ciph-sha-256-01.txt

               use Digest::SHA qw(hmac_sha256_hex);
               print hmac_sha256_hex("Hi There", chr(0x0b) x 32), "\n";


UNICODE AND SIDE EFFECTS

       Perl supports Unicode strings as of version 5.6.  Such strings may
       contain wide characters, namely, characters whose ordinal values are
       greater than 255.  This can cause problems for digest algorithms such
       as SHA that are specified to operate on sequences of bytes.

       The rule by which Digest::SHA handles a Unicode string is easy to
       state, but potentially confusing to grasp: the string is interpreted as
       a sequence of byte values, where each byte value is equal to the
       ordinal value (viz. code point) of its corresponding Unicode character.
       That way, the Unicode string 'abc' has exactly the same digest value as
       the ordinary string 'abc'.

       Since a wide character does not fit into a byte, the Digest::SHA
       routines croak if they encounter one.  Whereas if a Unicode string
       contains no wide characters, the module accepts it quite happily.  The
       following code illustrates the two cases:

               $str1 = pack('U*', (0..255));
               print sha1_hex($str1);          # ok

               $str2 = pack('U*', (0..256));
               print sha1_hex($str2);          # croaks

       Be aware that the digest routines silently convert UTF-8 input into its
       equivalent byte sequence in the native encoding (cf. utf8::downgrade).
       This side effect influences only the way Perl stores the data
       internally, but otherwise leaves the actual value of the data intact.


NIST STATEMENT ON SHA-1

       NIST acknowledges that the work of Prof. Xiaoyun Wang constitutes a
       practical collision attack on SHA-1.  Therefore, NIST encourages the
       rapid adoption of the SHA-2 hash functions (e.g. SHA-256) for
       applications requiring strong collision resistance, such as digital
       signatures.

       ref. <http://csrc.nist.gov/groups/ST/hash/statement.html>


PADDING OF BASE64 DIGESTS

       By convention, CPAN Digest modules do not pad their Base64 output.
       Problems can occur when feeding such digests to other software that
       expects properly padded Base64 encodings.

       For the time being, any necessary padding must be done by the user.
       Fortunately, this is a simple operation: if the length of a
       Base64-encoded digest isn't a multiple of 4, simply append "="
       characters to the end of the digest until it is:

               while (length($b64_digest) % 4) {
                       $b64_digest .= '=';
               }

       To illustrate, sha256_base64("abc") is computed to be

               ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0

       which has a length of 43.  So, the properly padded version is

               ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0=


EXPORT

       None by default.


EXPORTABLE FUNCTIONS

       Provided your C compiler supports a 64-bit type (e.g. the long long of
       C99, or __int64 used by Microsoft C/C++), all of these functions will
       be available for use.  Otherwise, you won't be able to perform the
       SHA-384 and SHA-512 transforms, both of which require 64-bit
       operations.

       Functional style

       sha1($data, ...)
       sha224($data, ...)
       sha256($data, ...)
       sha384($data, ...)
       sha512($data, ...)
       sha512224($data, ...)
       sha512256($data, ...)
           Logically joins the arguments into a single string, and returns its
           SHA-1/224/256/384/512 digest encoded as a binary string.

       sha1_hex($data, ...)
       sha224_hex($data, ...)
       sha256_hex($data, ...)
       sha384_hex($data, ...)
       sha512_hex($data, ...)
       sha512224_hex($data, ...)
       sha512256_hex($data, ...)
           Logically joins the arguments into a single string, and returns its
           SHA-1/224/256/384/512 digest encoded as a hexadecimal string.

       sha1_base64($data, ...)
       sha224_base64($data, ...)
       sha256_base64($data, ...)
       sha384_base64($data, ...)
       sha512_base64($data, ...)
       sha512224_base64($data, ...)
       sha512256_base64($data, ...)
           Logically joins the arguments into a single string, and returns its
           SHA-1/224/256/384/512 digest encoded as a Base64 string.

           It's important to note that the resulting string does not contain
           the padding characters typical of Base64 encodings.  This omission
           is deliberate, and is done to maintain compatibility with the
           family of CPAN Digest modules.  See "PADDING OF BASE64 DIGESTS" for
           details.

       OOP style

       new($alg)
           Returns a new Digest::SHA object.  Allowed values for $alg are 1,
           224, 256, 384, 512, 512224, or 512256.  It's also possible to use
           common string representations of the algorithm (e.g. "sha256",
           "SHA-384").  If the argument is missing, SHA-1 will be used by
           default.

           Invoking new as an instance method will reset the object to the
           initial state associated with $alg.  If the argument is missing,
           the object will continue using the same algorithm that was selected
           at creation.

       reset($alg)
           This method has exactly the same effect as new($alg).  In fact,
           reset is just an alias for new.

       hashsize
           Returns the number of digest bits for this object.  The values are
           160, 224, 256, 384, 512, 224, and 256 for SHA-1, SHA-224, SHA-256,
           SHA-384, SHA-512, SHA-512/224 and SHA-512/256, respectively.

       algorithm
           Returns the digest algorithm for this object.  The values are 1,
           224, 256, 384, 512, 512224, and 512256 for SHA-1, SHA-224, SHA-256,
           SHA-384, SHA-512, SHA-512/224, and SHA-512/256, respectively.

       clone
           Returns a duplicate copy of the object.

       add($data, ...)
           Logically joins the arguments into a single string, and uses it to
           update the current digest state.  In other words, the following
           statements have the same effect:

                   $sha->add("a"); $sha->add("b"); $sha->add("c");
                   $sha->add("a")->add("b")->add("c");
                   $sha->add("a", "b", "c");
                   $sha->add("abc");

           The return value is the updated object itself.

       add_bits($data, $nbits)
       add_bits($bits)
           Updates the current digest state by appending bits to it.  The
           return value is the updated object itself.

           The first form causes the most-significant $nbits of $data to be
           appended to the stream.  The $data argument is in the customary
           binary format used for Perl strings.

           The second form takes an ASCII string of "0" and "1" characters as
           its argument.  It's equivalent to

                   $sha->add_bits(pack("B*", $bits), length($bits));

           So, the following two statements do the same thing:

                   $sha->add_bits("111100001010");
                   $sha->add_bits("\xF0\xA0", 12);

           Note that SHA-1 and SHA-2 use most-significant-bit ordering for
           their internal state.  This means that

                   $sha3->add_bits("110");

           is equivalent to

                   $sha3->add_bits("1")->add_bits("1")->add_bits("0");

       addfile(*FILE)
           Reads from FILE until EOF, and appends that data to the current
           state.  The return value is the updated object itself.

       addfile($filename [, $mode])
           Reads the contents of $filename, and appends that data to the
           current state.  The return value is the updated object itself.

           By default, $filename is simply opened and read; no special modes
           or I/O disciplines are used.  To change this, set the optional
           $mode argument to one of the following values:

                   "b"     read file in binary mode

                   "U"     use universal newlines

                   "0"     use BITS mode

                   "p"     use portable mode (to be deprecated)

           The "U" mode is modeled on Python's "Universal Newlines" concept,
           whereby DOS and Mac OS line terminators are converted internally to
           UNIX newlines before processing.  This ensures consistent digest
           values when working simultaneously across multiple file systems.
           The "U" mode influences only text files, namely those passing
           Perl's -T test; binary files are processed with no translation
           whatsoever.

           The "p" mode differs from "U" only in that it treats "\r\r\n" as a
           single newline, a quirky feature designed to accommodate legacy
           applications that occasionally added an extra carriage return
           before DOS line terminators.  The "p" mode will be phased out
           eventually in favor of the cleaner and more well-established
           Universal Newlines concept.

           The BITS mode ("0") interprets the contents of $filename as a
           logical stream of bits, where each ASCII '0' or '1' character
           represents a 0 or 1 bit, respectively.  All other characters are
           ignored.  This provides a convenient way to calculate the digest
           values of partial-byte data by using files, rather than having to
           write separate programs employing the add_bits method.

       getstate
           Returns a string containing a portable, human-readable
           representation of the current SHA state.

       putstate($str)
           Returns a Digest::SHA object representing the SHA state contained
           in $str.  The format of $str matches the format of the output
           produced by method getstate.  If called as a class method, a new
           object is created; if called as an instance method, the object is
           reset to the state contained in $str.

       dump($filename)
           Writes the output of getstate to $filename.  If the argument is
           missing, or equal to the empty string, the state information will
           be written to STDOUT.

       load($filename)
           Returns a Digest::SHA object that results from calling putstate on
           the contents of $filename.  If the argument is missing, or equal to
           the empty string, the state information will be read from STDIN.

       digest
           Returns the digest encoded as a binary string.

           Note that the digest method is a read-once operation. Once it has
           been performed, the Digest::SHA object is automatically reset in
           preparation for calculating another digest value.  Call
           $sha->clone->digest if it's necessary to preserve the original
           digest state.

       hexdigest
           Returns the digest encoded as a hexadecimal string.

           Like digest, this method is a read-once operation.  Call
           $sha->clone->hexdigest if it's necessary to preserve the original
           digest state.

       b64digest
           Returns the digest encoded as a Base64 string.

           Like digest, this method is a read-once operation.  Call
           $sha->clone->b64digest if it's necessary to preserve the original
           digest state.

           It's important to note that the resulting string does not contain
           the padding characters typical of Base64 encodings.  This omission
           is deliberate, and is done to maintain compatibility with the
           family of CPAN Digest modules.  See "PADDING OF BASE64 DIGESTS" for
           details.

       HMAC-SHA-1/224/256/384/512

       hmac_sha1($data, $key)
       hmac_sha224($data, $key)
       hmac_sha256($data, $key)
       hmac_sha384($data, $key)
       hmac_sha512($data, $key)
       hmac_sha512224($data, $key)
       hmac_sha512256($data, $key)
           Returns the HMAC-SHA-1/224/256/384/512 digest of $data/$key, with
           the result encoded as a binary string.  Multiple $data arguments
           are allowed, provided that $key is the last argument in the list.

       hmac_sha1_hex($data, $key)
       hmac_sha224_hex($data, $key)
       hmac_sha256_hex($data, $key)
       hmac_sha384_hex($data, $key)
       hmac_sha512_hex($data, $key)
       hmac_sha512224_hex($data, $key)
       hmac_sha512256_hex($data, $key)
           Returns the HMAC-SHA-1/224/256/384/512 digest of $data/$key, with
           the result encoded as a hexadecimal string.  Multiple $data
           arguments are allowed, provided that $key is the last argument in
           the list.

       hmac_sha1_base64($data, $key)
       hmac_sha224_base64($data, $key)
       hmac_sha256_base64($data, $key)
       hmac_sha384_base64($data, $key)
       hmac_sha512_base64($data, $key)
       hmac_sha512224_base64($data, $key)
       hmac_sha512256_base64($data, $key)
           Returns the HMAC-SHA-1/224/256/384/512 digest of $data/$key, with
           the result encoded as a Base64 string.  Multiple $data arguments
           are allowed, provided that $key is the last argument in the list.

           It's important to note that the resulting string does not contain
           the padding characters typical of Base64 encodings.  This omission
           is deliberate, and is done to maintain compatibility with the
           family of CPAN Digest modules.  See "PADDING OF BASE64 DIGESTS" for
           details.


SEE ALSO

       Digest(3), Digest::SHA::PurePerl(3)

       The Secure Hash Standard (Draft FIPS PUB 180-4) can be found at:

       <http://csrc.nist.gov/publications/drafts/fips180-4/Draft-FIPS180-4_Feb2011.pdf>

       The Keyed-Hash Message Authentication Code (HMAC):

       <http://csrc.nist.gov/publications/fips/fips198/fips-198a.pdf>


AUTHOR

               Mark Shelor     <mshelor@cpan.org>


ACKNOWLEDGMENTS

       The author is particularly grateful to

               Gisle Aas
               H. Merijn Brand
               Sean Burke
               Chris Carey
               Alexandr Ciornii
               Jim Doble
               Thomas Drugeon
               Julius Duque
               Jeffrey Friedl
               Robert Gilmour
               Brian Gladman
               Jarkko Hietaniemi
               Adam Kennedy
               Mark Lawrence
               Andy Lester
               Alex Muntada
               Steve Peters
               Chris Skiscim
               Martin Thurn
               Gunnar Wolf
               Adam Woodbury

       "who by trained skill rescued life from such great billows and such
       thick darkness and moored it in so perfect a calm and in so brilliant a
       light" - Lucretius


COPYRIGHT AND LICENSE

       Copyright (C) 2003-2016 Mark Shelor

       This library is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself.

       perlartistic



perl v5.26.1                      2017-07-18                  Digest::SHA(3pm)

perl 5.26.1 - Generated Sat Nov 4 12:38:25 CDT 2017
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