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<title>GnuTLS 3.5.3: Verifying a certificate in the context of TLS session</title>
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<a name="Verifying-a-certificate-in-the-context-of-TLS-session"></a>
<div class="header">
<p>
Next: <a href="Verification-using-PKCS11.html#Verification-using-PKCS11" accesskey="n" rel="next">Verification using PKCS11</a>, Previous: <a href="Verifying-X_002e509-certificate-paths.html#Verifying-X_002e509-certificate-paths" accesskey="p" rel="prev">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">4.1.1.8 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_005ftrust_005fdir">gnutls_certificate_set_x509_trust_dir</a> (gnutls_certificate_credentials_t <var>cred</var>, const char * <var>ca_dir</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>These functions allow the specification of the trusted certificate authorities, either
via a file, a directory or use the system-specified certificate authorities.
Unless the authorities are application specific, it is generally recommended
to use the system trust storage (see <a href="Core-TLS-API.html#gnutls_005fcertificate_005fset_005fx509_005fsystem_005ftrust">gnutls_certificate_set_x509_system_trust</a>).
</p>
<p>Unlike the previous section it is not required to setup a trusted list, and there
are two approaches to verify the peer’s certificate and identity.
The recommended in GnuTLS 3.5.0 and later is via the <a href="Core-TLS-API.html#gnutls_005fsession_005fset_005fverify_005fcert">gnutls_session_set_verify_cert</a>,
but for older GnuTLS versions you may use an explicit callback set via
<a href="Core-TLS-API.html#gnutls_005fcertificate_005fset_005fverify_005ffunction">gnutls_certificate_set_verify_function</a> and then utilize
<a href="Core-TLS-API.html#gnutls_005fcertificate_005fverify_005fpeers3">gnutls_certificate_verify_peers3</a> for verification.
The reported verification status is identical to the verification functions described
in the previous section.
</p>
<p>Note that in certain cases it is required to check the marked purpose of
the end certificate (e.g. <code>GNUTLS_KP_TLS_WWW_SERVER</code>); in these cases
the more advanced <a href="Core-TLS-API.html#gnutls_005fsession_005fset_005fverify_005fcert2">gnutls_session_set_verify_cert2</a> and
<a href="Core-TLS-API.html#gnutls_005fcertificate_005fverify_005fpeers">gnutls_certificate_verify_peers</a> should be used instead.
</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_005fcrt2">gnutls_x509_trust_list_verify_crt2</a> the
flags are passed directly, but for
<a href="Core-TLS-API.html#gnutls_005fcertificate_005fverify_005fpeers3">gnutls_certificate_verify_peers3</a>, the flags are set using
<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 normally be disabled,
unless you know what this means.
</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.
</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>
<dt><code>GNUTLS_VERIFY_DO_NOT_ALLOW_WILDCARDS</code></dt>
<dd><p>When including a hostname
check in the verification, do not consider any wildcards.
</p></dd>
<dt><code>GNUTLS_VERIFY_USE_TLS1_RSA</code></dt>
<dd><p>This indicates that a (raw) RSA signature is provided
as in the TLS 1.0 protocol. Not all functions accept this flag.
</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>
Next: <a href="Verification-using-PKCS11.html#Verification-using-PKCS11" accesskey="n" rel="next">Verification using PKCS11</a>, Previous: <a href="Verifying-X_002e509-certificate-paths.html#Verifying-X_002e509-certificate-paths" accesskey="p" rel="prev">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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