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<a name="Verifying-a-certificate-in-the-context-of-TLS-session"></a>
<div class="header">
<p>
Previous: <a href="Verifying-X_002e509-certificate-paths.html#Verifying-X_002e509-certificate-paths" accesskey="p" rel="previous">Verifying X.509 certificate paths</a>, Up: <a href="X_002e509-certificates.html#X_002e509-certificates" accesskey="u" rel="up">X.509 certificates</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Function-and-Data-Index.html#Function-and-Data-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Verifying-a-certificate-in-the-context-of-TLS-session-1"></a>
<h4 class="subsubsection">4.1.1.6 Verifying a certificate in the context of TLS session</h4>
<a name="index-verifying-certificate-paths-1"></a>
<a name="index-gnutls_005fcertificate_005fverify_005fflags"></a>
<p>When operating in the context of a TLS session, the trusted certificate
authority list may also be set using:
</p><dl compact="compact">
<dt><code><var>int</var> <a href="Core-TLS-API.html#gnutls_005fcertificate_005fset_005fx509_005ftrust_005ffile">gnutls_certificate_set_x509_trust_file</a> (gnutls_certificate_credentials_t <var>cred</var>, const char * <var>cafile</var>, gnutls_x509_crt_fmt_t <var>type</var>)</code></dt>
<dt><code><var>int</var> <a href="Core-TLS-API.html#gnutls_005fcertificate_005fset_005fx509_005fcrl_005ffile">gnutls_certificate_set_x509_crl_file</a> (gnutls_certificate_credentials_t <var>res</var>, const char * <var>crlfile</var>, gnutls_x509_crt_fmt_t <var>type</var>)</code></dt>
<dt><code><var>int</var> <a href="Core-TLS-API.html#gnutls_005fcertificate_005fset_005fx509_005fsystem_005ftrust">gnutls_certificate_set_x509_system_trust</a> (gnutls_certificate_credentials_t <var>cred</var>)</code></dt>
</dl>
<p>Then it is not required to setup a trusted list as above.
The function <a href="Core-TLS-API.html#gnutls_005fcertificate_005fverify_005fpeers3">gnutls_certificate_verify_peers3</a>
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.
</p>
<p>There is also the possibility to pass some input to the verification
functions in the form of flags. For <a href="X509-certificate-API.html#gnutls_005fx509_005ftrust_005flist_005fverify_005fcrt">gnutls_x509_trust_list_verify_crt</a> the
flags are passed straightforward, but
<a href="Core-TLS-API.html#gnutls_005fcertificate_005fverify_005fpeers3">gnutls_certificate_verify_peers3</a> depends on the flags set by
calling <a href="Core-TLS-API.html#gnutls_005fcertificate_005fset_005fverify_005fflags">gnutls_certificate_set_verify_flags</a>. All the available
flags are part of the enumeration
<code>gnutls_certificate_verify_flags</code> shown in <a href="#gnutls_005fcertificate_005fverify_005fflags">Figure 4.3</a>.
</p>
<div class="float"><a name="gnutls_005fcertificate_005fverify_005fflags"></a>
<dl compact="compact">
<dt><code>GNUTLS_VERIFY_DISABLE_CA_SIGN</code></dt>
<dd><p>If set a signer does not have to be
a certificate authority. This flag should normaly be disabled,
unless you know what this means.
</p></dd>
<dt><code>GNUTLS_VERIFY_ALLOW_X509_V1_CA_CRT</code></dt>
<dd><p>Allow trusted CA certificates
with version 1. This is safer than <code>GNUTLS_VERIFY_ALLOW_ANY_X509_V1_CA_CRT</code> ,
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.
</p></dd>
<dt><code>GNUTLS_VERIFY_DO_NOT_ALLOW_SAME</code></dt>
<dd><p>If a certificate is not signed by
anyone trusted but exists in the trusted CA list do not treat it
as trusted.
</p></dd>
<dt><code>GNUTLS_VERIFY_ALLOW_ANY_X509_V1_CA_CRT</code></dt>
<dd><p>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
<code>GNUTLS_VERIFY_ALLOW_X509_V1_CA_CRT</code> .
</p></dd>
<dt><code>GNUTLS_VERIFY_ALLOW_SIGN_RSA_MD2</code></dt>
<dd><p>Allow certificates to be signed
using the broken MD2 algorithm.
</p></dd>
<dt><code>GNUTLS_VERIFY_ALLOW_SIGN_RSA_MD5</code></dt>
<dd><p>Allow certificates to be signed
using the broken MD5 algorithm.
</p></dd>
<dt><code>GNUTLS_VERIFY_DISABLE_TIME_CHECKS</code></dt>
<dd><p>Disable checking of activation
and expiration validity periods of certificate chains. Don’t set
this unless you understand the security implications.
</p></dd>
<dt><code>GNUTLS_VERIFY_DISABLE_TRUSTED_TIME_CHECKS</code></dt>
<dd><p>If set a signer in the trusted
list is never checked for expiration or activation.
</p></dd>
<dt><code>GNUTLS_VERIFY_DO_NOT_ALLOW_X509_V1_CA_CRT</code></dt>
<dd><p>Do not allow trusted CA
certificates that have version 1. This option is to be used
to deprecate all certificates of version 1.
</p></dd>
<dt><code>GNUTLS_VERIFY_DISABLE_CRL_CHECKS</code></dt>
<dd><p>Disable checking for validity
using certificate revocation lists or the available OCSP data.
</p></dd>
<dt><code>GNUTLS_VERIFY_ALLOW_UNSORTED_CHAIN</code></dt>
<dd><p>A certificate chain is tolerated
if unsorted (the case with many TLS servers out there). This is the
default since GnuTLS 3.1.4.
</p></dd>
<dt><code>GNUTLS_VERIFY_DO_NOT_ALLOW_UNSORTED_CHAIN</code></dt>
<dd><p>Do not tolerate an unsorted
certificate chain.
</p></dd>
</dl>
<div class="float-caption"><p><strong>Figure 4.3: </strong>The <code>gnutls_certificate_verify_flags</code> enumeration.</p></div></div>
<hr>
<div class="header">
<p>
Previous: <a href="Verifying-X_002e509-certificate-paths.html#Verifying-X_002e509-certificate-paths" accesskey="p" rel="previous">Verifying X.509 certificate paths</a>, Up: <a href="X_002e509-certificates.html#X_002e509-certificates" accesskey="u" rel="up">X.509 certificates</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Function-and-Data-Index.html#Function-and-Data-Index" title="Index" rel="index">Index</a>]</p>
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