info gnutls

4.1.1.6 Verifying a certificate in the context of TLS session

When operating in the context of a TLS session, the trusted certificate authority list may also be set using:

int gnutls_certificate_set_x509_trust_file (gnutls_certificate_credentials_t cred, const char * cafile, gnutls_x509_crt_fmt_t type)
int gnutls_certificate_set_x509_crl_file (gnutls_certificate_credentials_t res, const char * crlfile, gnutls_x509_crt_fmt_t type)
int gnutls_certificate_set_x509_system_trust (gnutls_certificate_credentials_t cred)

Then it is not required to setup a trusted list as above. The function gnutls_certificate_verify_peers3 may then be used to verify the peer’s certificate chain and identity. The flags are set similarly to the verification functions in the previous section.

There is also the possibility to pass some input to the verification functions in the form of flags. For gnutls_x509_trust_list_verify_crt the flags are passed straightforward, but gnutls_certificate_verify_peers3 depends on the flags set by calling gnutls_certificate_set_verify_flags. All the available flags are part of the enumeration gnutls_certificate_verify_flags shown in Figure 4.3.

GNUTLS_VERIFY_DISABLE_CA_SIGN: If set a signer does not have to be a certificate authority. This flag should normally be disabled, unless you know what this means.
GNUTLS_VERIFY_ALLOW_X509_V1_CA_CRT: Allow trusted CA certificates with version 1. This is safer than GNUTLS_VERIFY_ALLOW_ANY_X509_V1_CA_CRT , and should be used instead. That way only signers in your trusted list will be allowed to have certificates of version 1. This is the default.
GNUTLS_VERIFY_DO_NOT_ALLOW_SAME: If a certificate is not signed by anyone trusted but exists in the trusted CA list do not treat it as trusted.
GNUTLS_VERIFY_ALLOW_ANY_X509_V1_CA_CRT: Allow CA certificates that have version 1 (both root and intermediate). This might be dangerous since those haven’t the basicConstraints extension. Must be used in combination with GNUTLS_VERIFY_ALLOW_X509_V1_CA_CRT .
GNUTLS_VERIFY_ALLOW_SIGN_RSA_MD2: Allow certificates to be signed using the broken MD2 algorithm.
GNUTLS_VERIFY_ALLOW_SIGN_RSA_MD5: Allow certificates to be signed using the broken MD5 algorithm.
GNUTLS_VERIFY_DISABLE_TIME_CHECKS: Disable checking of activation and expiration validity periods of certificate chains. Don’t set this unless you understand the security implications.
GNUTLS_VERIFY_DISABLE_TRUSTED_TIME_CHECKS: If set a signer in the trusted list is never checked for expiration or activation.
GNUTLS_VERIFY_DO_NOT_ALLOW_X509_V1_CA_CRT: Do not allow trusted CA certificates that have version 1. This option is to be used to deprecate all certificates of version 1.
GNUTLS_VERIFY_DISABLE_CRL_CHECKS: Disable checking for validity using certificate revocation lists or the available OCSP data.
GNUTLS_VERIFY_ALLOW_UNSORTED_CHAIN: A certificate chain is tolerated if unsorted (the case with many TLS servers out there). This is the default since GnuTLS 3.1.4.
GNUTLS_VERIFY_DO_NOT_ALLOW_UNSORTED_CHAIN: Do not tolerate an unsorted certificate chain.

Figure 4.3: The gnutls_certificate_verify_flags enumeration.

This document was generated on February 9, 2014 using texi2html 5.0.