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<h1><a href="../index.html">MIT Kerberos Documentation</a></h1>
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<div class="section" id="otp-preauthentication">
<h1>OTP Preauthentication<a class="headerlink" href="#otp-preauthentication" title="Permalink to this headline">¶</a></h1>
<p>OTP is a preauthentication mechanism for Kerberos 5 which uses One
Time Passwords (OTP) to authenticate the client to the KDC. The OTP
is passed to the KDC over an encrypted FAST channel in clear-text.
The KDC uses the password along with per-user configuration to proxy
the request to a third-party RADIUS system. This enables
out-of-the-box compatibility with a large number of already widely
deployed proprietary systems.</p>
<p>Additionally, our implementation of the OTP system allows for the
passing of RADIUS requests over a UNIX domain stream socket. This
permits the use of a local companion daemon which can handle the
details of authentication.</p>
<div class="section" id="defining-token-types">
<h2>Defining token types<a class="headerlink" href="#defining-token-types" title="Permalink to this headline">¶</a></h2>
<p>Token types are defined in either krb5.conf or kdc.conf according to
the following format:</p>
<div class="highlight-python"><pre>[otp]
<name> = {
server = <host:port or filename> (default: $KDCDIR/<name>.socket)
secret = <filename>
timeout = <integer> (default: 5 [seconds])
retries = <integer> (default: 3)
strip_realm = <boolean> (default: true)
}</pre>
</div>
<p>If the server field begins with ‘/’, it will be interpreted as a UNIX
socket. Otherwise, it is assumed to be in the format host:port. When
a UNIX domain socket is specified, the secret field is optional and an
empty secret is used by default.</p>
<p>When forwarding the request over RADIUS, by default the principal is
used in the User-Name attribute of the RADIUS packet. The strip_realm
parameter controls whether the principal is forwarded with or without
the realm portion.</p>
</div>
<div class="section" id="the-default-token-type">
<h2>The default token type<a class="headerlink" href="#the-default-token-type" title="Permalink to this headline">¶</a></h2>
<p>A default token type is used internally when no token type is specified for a
given user. It is defined as follows:</p>
<div class="highlight-python"><pre>[otp]
DEFAULT = {
strip_realm = false
}</pre>
</div>
<p>The administrator may override the internal <tt class="docutils literal"><span class="pre">DEFAULT</span></tt> token type
simply by defining a configuration with the same name.</p>
</div>
<div class="section" id="token-instance-configuration">
<h2>Token instance configuration<a class="headerlink" href="#token-instance-configuration" title="Permalink to this headline">¶</a></h2>
<p>To enable OTP for a client principal, the administrator must define
the <strong>otp</strong> string attribute for that principal. The <strong>otp</strong> user
string is a JSON string of the format:</p>
<div class="highlight-python"><pre>[{
"type": <string>,
"username": <string>
}, ...]</pre>
</div>
<p>This is an array of token objects. Both fields of token objects are
optional. The <strong>type</strong> field names the token type of this token; if
not specified, it defaults to <tt class="docutils literal"><span class="pre">DEFAULT</span></tt>. The <strong>username</strong> field
specifies the value to be sent in the User-Name RADIUS attribute. If
not specified, the principal name is sent, with or without realm as
defined in the token type.</p>
<p>For ease of configuration, an empty array (<tt class="docutils literal"><span class="pre">[]</span></tt>) is treated as
equivalent to one DEFAULT token (<tt class="docutils literal"><span class="pre">[{}]</span></tt>).</p>
</div>
<div class="section" id="other-considerations">
<h2>Other considerations<a class="headerlink" href="#other-considerations" title="Permalink to this headline">¶</a></h2>
<ol class="arabic simple">
<li>FAST is required for OTP to work.</li>
</ol>
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<h2>On this page</h2>
<ul>
<li><a class="reference internal" href="#">OTP Preauthentication</a><ul>
<li><a class="reference internal" href="#defining-token-types">Defining token types</a></li>
<li><a class="reference internal" href="#the-default-token-type">The default token type</a></li>
<li><a class="reference internal" href="#token-instance-configuration">Token instance configuration</a></li>
<li><a class="reference internal" href="#other-considerations">Other considerations</a></li>
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<li class="toctree-l2"><a class="reference internal" href="install.html">Installation guide</a></li>
<li class="toctree-l2"><a class="reference internal" href="conf_files/index.html">Configuration Files</a></li>
<li class="toctree-l2"><a class="reference internal" href="realm_config.html">Realm configuration decisions</a></li>
<li class="toctree-l2"><a class="reference internal" href="database.html">Database administration</a></li>
<li class="toctree-l2"><a class="reference internal" href="lockout.html">Account lockout</a></li>
<li class="toctree-l2"><a class="reference internal" href="conf_ldap.html">Configuring Kerberos with OpenLDAP back-end</a></li>
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<li class="toctree-l2"><a class="reference internal" href="pkinit.html">PKINIT configuration</a></li>
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