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<h1>PKINIT freshness tokens<a class="headerlink" href="#pkinit-freshness-tokens" title="Permalink to this headline">ΒΆ</a></h1>
<p><span class="target" id="index-0"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc8070.html"><strong>RFC 8070</strong></a> specifies a pa-data type PA_AS_FRESHNESS, which clients
should reflect within signed PKINIT data to prove recent access to the
client certificate private key. The contents of a freshness token are
left to the KDC implementation. The MIT krb5 KDC uses the following
format for freshness tokens (starting in release 1.17):</p>
<ul class="simple">
<li>a four-byte big-endian POSIX timestamp</li>
<li>a four-byte big-endian key version number</li>
<li>an <span class="target" id="index-1"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc3961.html"><strong>RFC 3961</strong></a> checksum, with no ASN.1 wrapper</li>
</ul>
<p>The checksum is computed using the first key in the local krbtgt
principal entry for the realm (e.g. <code class="docutils literal notranslate"><span class="pre">krbtgt/KRBTEST.COM@KRBTEST.COM</span></code>
if the request is to the <code class="docutils literal notranslate"><span class="pre">KRBTEST.COM</span></code> realm) of the indicated key
version. The checksum type must be the mandatory checksum type for
the encryption type of the krbtgt key. The key usage value for the
checksum is 514.</p>
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