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<title>GnuTLS 3.5.4: PSK credentials</title>
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<a name="PSK-credentials"></a>
<div class="header">
<p>
Next: <a href="Anonymous-credentials.html#Anonymous-credentials" accesskey="n" rel="next">Anonymous credentials</a>, Previous: <a href="SRP-credentials.html#SRP-credentials" accesskey="p" rel="prev">SRP credentials</a>, Up: <a href="Associating-the-credentials.html#Associating-the-credentials" accesskey="u" rel="up">Associating the credentials</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="PSK"></a>
<h4 class="subsection">6.4.3 PSK</h4>
<p>The initialization functions in PSK credentials differ between
client and server.
</p>
<dl compact="compact">
<dt><code><var>int</var> <a href="Core-TLS-API.html#gnutls_005fpsk_005fallocate_005fserver_005fcredentials">gnutls_psk_allocate_server_credentials</a> (gnutls_psk_server_credentials_t * <var>sc</var>)</code></dt>
<dt><code><var>int</var> <a href="Core-TLS-API.html#gnutls_005fpsk_005fallocate_005fclient_005fcredentials">gnutls_psk_allocate_client_credentials</a> (gnutls_psk_client_credentials_t * <var>sc</var>)</code></dt>
<dt><code><var>void</var> <a href="Core-TLS-API.html#gnutls_005fpsk_005ffree_005fserver_005fcredentials">gnutls_psk_free_server_credentials</a> (gnutls_psk_server_credentials_t <var>sc</var>)</code></dt>
<dt><code><var>void</var> <a href="Core-TLS-API.html#gnutls_005fpsk_005ffree_005fclient_005fcredentials">gnutls_psk_free_client_credentials</a> (gnutls_psk_client_credentials_t <var>sc</var>)</code></dt>
</dl>
<p>Clients supporting <acronym>PSK</acronym> should supply the username and key
before a TLS session is established. Alternatively
<a href="Core-TLS-API.html#gnutls_005fpsk_005fset_005fclient_005fcredentials_005ffunction">gnutls_psk_set_client_credentials_function</a> can be used to
specify a callback function. This has the
advantage that the callback will be called only if <acronym>PSK</acronym> has
been negotiated.
</p>
<dl compact="compact">
<dt><code><var>int</var> <a href="Core-TLS-API.html#gnutls_005fpsk_005fset_005fclient_005fcredentials">gnutls_psk_set_client_credentials</a> (gnutls_psk_client_credentials_t <var>res</var>, const char * <var>username</var>, const gnutls_datum_t * <var>key</var>, gnutls_psk_key_flags <var>flags</var>)</code></dt>
</dl>
<dl>
<dt><a name="index-gnutls_005fpsk_005fset_005fclient_005fcredentials_005ffunction"></a>Function: <em>void</em> <strong>gnutls_psk_set_client_credentials_function</strong> <em>(gnutls_psk_client_credentials_t <var>cred</var>, gnutls_psk_client_credentials_function * <var>func</var>)</em></dt>
<dd><p><var>cred</var>: is a <code>gnutls_psk_server_credentials_t</code> type.
</p>
<p><var>func</var>: is the callback function
</p>
<p>This function can be used to set a callback to retrieve the username and
password for client PSK authentication.
The callback’s function form is:
int (*callback)(gnutls_session_t, char** username,
gnutls_datum_t* key);
</p>
<p>The <code>username</code> and <code>key</code> ->data must be allocated using <code>gnutls_malloc()</code> .
<code>username</code> should be ASCII strings or UTF-8 strings prepared using
the "SASLprep" profile of "stringprep".
</p>
<p>The callback function will be called once per handshake.
</p>
<p>The callback function should return 0 on success.
-1 indicates an error.
</p></dd></dl>
<p>In server side the default behavior of <acronym>GnuTLS</acronym> is to read
the usernames and <acronym>PSK</acronym> keys from a password file. The
password file should contain usernames and keys in hexadecimal
format. The name of the password file can be stored to the credentials
structure by calling <a href="Core-TLS-API.html#gnutls_005fpsk_005fset_005fserver_005fcredentials_005ffile">gnutls_psk_set_server_credentials_file</a>. If
a different password file format is to be used, then
a callback should be set instead by <a href="Core-TLS-API.html#gnutls_005fpsk_005fset_005fserver_005fcredentials_005ffunction">gnutls_psk_set_server_credentials_function</a>.
</p>
<p>The server can help the client chose a suitable username and password,
by sending a hint. Note that there is no common profile for the PSK hint and applications
are discouraged to use it.
A server, may specify the hint by calling
<a href="Core-TLS-API.html#gnutls_005fpsk_005fset_005fserver_005fcredentials_005fhint">gnutls_psk_set_server_credentials_hint</a>. The client can retrieve
the hint, for example in the callback function, using
<a href="Core-TLS-API.html#gnutls_005fpsk_005fclient_005fget_005fhint">gnutls_psk_client_get_hint</a>.
</p>
<dl>
<dt><a name="index-gnutls_005fpsk_005fset_005fserver_005fcredentials_005ffile"></a>Function: <em>int</em> <strong>gnutls_psk_set_server_credentials_file</strong> <em>(gnutls_psk_server_credentials_t <var>res</var>, const char * <var>password_file</var>)</em></dt>
<dd><p><var>res</var>: is a <code>gnutls_psk_server_credentials_t</code> type.
</p>
<p><var>password_file</var>: is the PSK password file (passwd.psk)
</p>
<p>This function sets the password file, in a
<code>gnutls_psk_server_credentials_t</code> type. This password file
holds usernames and keys and will be used for PSK authentication.
</p>
<p><strong>Returns:</strong> On success, <code>GNUTLS_E_SUCCESS</code> (0) is returned, otherwise
an error code is returned.
</p></dd></dl>
<dl compact="compact">
<dt><code><var>void</var> <a href="Core-TLS-API.html#gnutls_005fpsk_005fset_005fserver_005fcredentials_005ffunction">gnutls_psk_set_server_credentials_function</a> (gnutls_psk_server_credentials_t <var>cred</var>, gnutls_psk_server_credentials_function * <var>func</var>)</code></dt>
<dt><code><var>int</var> <a href="Core-TLS-API.html#gnutls_005fpsk_005fset_005fserver_005fcredentials_005fhint">gnutls_psk_set_server_credentials_hint</a> (gnutls_psk_server_credentials_t <var>res</var>, const char * <var>hint</var>)</code></dt>
<dt><code><var>const char *</var> <a href="Core-TLS-API.html#gnutls_005fpsk_005fclient_005fget_005fhint">gnutls_psk_client_get_hint</a> (gnutls_session_t <var>session</var>)</code></dt>
</dl>
<hr>
<div class="header">
<p>
Next: <a href="Anonymous-credentials.html#Anonymous-credentials" accesskey="n" rel="next">Anonymous credentials</a>, Previous: <a href="SRP-credentials.html#SRP-credentials" accesskey="p" rel="prev">SRP credentials</a>, Up: <a href="Associating-the-credentials.html#Associating-the-credentials" accesskey="u" rel="up">Associating the credentials</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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