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<title>GnuTLS 3.4.9: SRTP</title>
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<a name="SRTP"></a>
<div class="header">
<p>
Next: <a href="Application-Layer-Protocol-Negotiation-_0028ALPN_0029.html#Application-Layer-Protocol-Negotiation-_0028ALPN_0029" accesskey="n" rel="next">Application Layer Protocol Negotiation (ALPN)</a>, Previous: <a href="OCSP-status-request.html#OCSP-status-request" accesskey="p" rel="prev">OCSP status request</a>, Up: <a href="TLS-Extensions.html#TLS-Extensions" accesskey="u" rel="up">TLS Extensions</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="SRTP-1"></a>
<h4 class="subsection">3.6.7 SRTP</h4>
<a name="index-SRTP"></a>
<a name="index-Secure-RTP"></a>
<p>The TLS protocol was extended in [<em>RFC5764</em>] to provide keying material to the
Secure RTP (SRTP) protocol. The SRTP protocol provides an encapsulation of encrypted
data that is optimized for voice data. With the SRTP TLS extension two peers can
negotiate keys using TLS or DTLS and obtain keying material for use with SRTP. The
available SRTP profiles are listed below.
</p>
<div class="float"><a name="gnutls_005fsrtp_005fprofile_005ft"></a>
<dl compact="compact">
<dt><code>GNUTLS_SRTP_AES128_CM_HMAC_SHA1_80</code></dt>
<dd><p>128 bit AES with a 80 bit HMAC-SHA1
</p></dd>
<dt><code>GNUTLS_SRTP_AES128_CM_HMAC_SHA1_32</code></dt>
<dd><p>128 bit AES with a 32 bit HMAC-SHA1
</p></dd>
<dt><code>GNUTLS_SRTP_NULL_HMAC_SHA1_80</code></dt>
<dd><p>NULL cipher with a 80 bit HMAC-SHA1
</p></dd>
<dt><code>GNUTLS_SRTP_NULL_HMAC_SHA1_32</code></dt>
<dd><p>NULL cipher with a 32 bit HMAC-SHA1
</p></dd>
</dl>
<div class="float-caption"><p><strong>Figure 3.3: </strong>Supported SRTP profiles</p></div></div>
<p>To enable use the following functions.
</p>
<dl compact="compact">
<dt><code><var>int</var> <a href="Core-TLS-API.html#gnutls_005fsrtp_005fset_005fprofile">gnutls_srtp_set_profile</a> (gnutls_session_t <var>session</var>, gnutls_srtp_profile_t <var>profile</var>)</code></dt>
<dt><code><var>int</var> <a href="Core-TLS-API.html#gnutls_005fsrtp_005fset_005fprofile_005fdirect">gnutls_srtp_set_profile_direct</a> (gnutls_session_t <var>session</var>, const char * <var>profiles</var>, const char ** <var>err_pos</var>)</code></dt>
</dl>
<p>To obtain the negotiated keys use the function below.
</p>
<dl>
<dt><a name="index-gnutls_005fsrtp_005fget_005fkeys"></a>Function: <em>int</em> <strong>gnutls_srtp_get_keys</strong> <em>(gnutls_session_t <var>session</var>, void * <var>key_material</var>, unsigned int <var>key_material_size</var>, gnutls_datum_t * <var>client_key</var>, gnutls_datum_t * <var>client_salt</var>, gnutls_datum_t * <var>server_key</var>, gnutls_datum_t * <var>server_salt</var>)</em></dt>
<dd><p><var>session</var>: is a <code>gnutls_session_t</code> type.
</p>
<p><var>key_material</var>: Space to hold the generated key material
</p>
<p><var>key_material_size</var>: The maximum size of the key material
</p>
<p><var>client_key</var>: The master client write key, pointing inside the key material
</p>
<p><var>client_salt</var>: The master client write salt, pointing inside the key material
</p>
<p><var>server_key</var>: The master server write key, pointing inside the key material
</p>
<p><var>server_salt</var>: The master server write salt, pointing inside the key material
</p>
<p>This is a helper function to generate the keying material for SRTP.
It requires the space of the key material to be pre-allocated (should be at least
2x the maximum key size and salt size). The <code>client_key</code> , <code>client_salt</code> , <code>server_key</code> and <code>server_salt</code> are convenience datums that point inside the key material. They may
be <code>NULL</code> .
</p>
<p><strong>Returns:</strong> On success the size of the key material is returned,
otherwise, <code>GNUTLS_E_SHORT_MEMORY_BUFFER</code> if the buffer given is not
sufficient, or a negative error code.
</p>
<p>Since 3.1.4
</p></dd></dl>
<p>Other helper functions are listed below.
</p>
<dl compact="compact">
<dt><code><var>int</var> <a href="Core-TLS-API.html#gnutls_005fsrtp_005fget_005fselected_005fprofile">gnutls_srtp_get_selected_profile</a> (gnutls_session_t <var>session</var>, gnutls_srtp_profile_t * <var>profile</var>)</code></dt>
<dt><code><var>const char *</var> <a href="Core-TLS-API.html#gnutls_005fsrtp_005fget_005fprofile_005fname">gnutls_srtp_get_profile_name</a> (gnutls_srtp_profile_t <var>profile</var>)</code></dt>
<dt><code><var>int</var> <a href="Core-TLS-API.html#gnutls_005fsrtp_005fget_005fprofile_005fid">gnutls_srtp_get_profile_id</a> (const char * <var>name</var>, gnutls_srtp_profile_t * <var>profile</var>)</code></dt>
</dl>
<hr>
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<p>
Next: <a href="Application-Layer-Protocol-Negotiation-_0028ALPN_0029.html#Application-Layer-Protocol-Negotiation-_0028ALPN_0029" accesskey="n" rel="next">Application Layer Protocol Negotiation (ALPN)</a>, Previous: <a href="OCSP-status-request.html#OCSP-status-request" accesskey="p" rel="prev">OCSP status request</a>, Up: <a href="TLS-Extensions.html#TLS-Extensions" accesskey="u" rel="up">TLS Extensions</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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