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<title>GnuTLS 3.2.0: Keying Material Exporters</title>
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Next: <a href="Channel-Bindings.html#Channel-Bindings" accesskey="n" rel="next">Channel Bindings</a>, Previous: <a href="Parameter-generation.html#Parameter-generation" accesskey="p" rel="previous">Parameter generation</a>, Up: <a href="Advanced-topics.html#Advanced-topics" accesskey="u" rel="up">Advanced topics</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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<hr>
<a name="Keying-material-exporters"></a>
<h4 class="subsection">6.12.4 Keying material exporters</h4>
<a name="index-keying-material-exporters"></a>
<a name="index-exporting-keying-material"></a>
<p>The TLS PRF can be used by other protocols to derive keys based on
the TLS master secret. The API to use is <a href="Core-TLS-API.html#gnutls_005fprf">gnutls_prf</a>. The
function needs to be provided with the label in the parameter
<code>label</code>, and the extra data to mix in the
<code>extra</code> parameter. Depending on whether you want to mix in the
client or server random data first, you can set the
<code>server_random_first</code> parameter.
</p>
<p>For example, after establishing a TLS session using
<a href="Core-TLS-API.html#gnutls_005fhandshake">gnutls_handshake</a>, you can invoke the TLS PRF with this call:
</p>
<div class="example">
<pre class="example">#define MYLABEL "EXPORTER-FOO"
#define MYCONTEXT "some context data"
char out[32];
rc = gnutls_prf (session, strlen (MYLABEL), MYLABEL, 0,
strlen (MYCONTEXT), MYCONTEXT, 32, out);
</pre></div>
<p>If you don’t want to mix in the client/server random, there is a
low-level TLS PRF interface called <a href="Core-TLS-API.html#gnutls_005fprf_005fraw">gnutls_prf_raw</a>.
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