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<h1><a href="../index.html">MIT Kerberos Documentation</a></h1>
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<div class="section" id="unix-application-servers">
<h1>UNIX Application Servers<a class="headerlink" href="#unix-application-servers" title="Permalink to this headline">¶</a></h1>
<p>An application server is a host that provides one or more services
over the network. Application servers can be “secure” or “insecure.”
A “secure” host is set up to require authentication from every client
connecting to it. An “insecure” host will still provide Kerberos
authentication, but will also allow unauthenticated clients to
connect.</p>
<p>If you have Kerberos V5 installed on all of your client machines, MIT
recommends that you make your hosts secure, to take advantage of the
security that Kerberos authentication affords. However, if you have
some clients that do not have Kerberos V5 installed, you can run an
insecure server, and still take advantage of Kerberos V5’s single
sign-on capability.</p>
<div class="section" id="the-keytab-file">
<span id="keytab-file"></span><h2>The keytab file<a class="headerlink" href="#the-keytab-file" title="Permalink to this headline">¶</a></h2>
<p>All Kerberos server machines need a keytab file to authenticate to the
KDC. By default on UNIX-like systems this file is named <code class="docutils literal notranslate"><span class="pre">FILE:/etc/krb5.keytab</span></code>.
The keytab file is an local copy of the host’s key. The keytab file
is a potential point of entry for a break-in, and if compromised,
would allow unrestricted access to its host. The keytab file should
be readable only by root, and should exist only on the machine’s local
disk. The file should not be part of any backup of the machine,
unless access to the backup data is secured as tightly as access to
the machine’s root password.</p>
<p>In order to generate a keytab for a host, the host must have a
principal in the Kerberos database. The procedure for adding hosts to
the database is described fully in <a class="reference internal" href="database.html#add-mod-del-princs"><span class="std std-ref">Adding, modifying and deleting principals</span></a>. (See
<a class="reference internal" href="install_kdc.html#replica-host-key"><span class="std std-ref">Create host keytabs for replica KDCs</span></a> for a brief description.) The keytab is
generated by running <a class="reference internal" href="admin_commands/kadmin_local.html#kadmin-1"><span class="std std-ref">kadmin</span></a> and issuing the <a class="reference internal" href="admin_commands/kadmin_local.html#ktadd"><span class="std std-ref">ktadd</span></a>
command.</p>
<p>For example, to generate a keytab file to allow the host
<code class="docutils literal notranslate"><span class="pre">trillium.mit.edu</span></code> to authenticate for the services host, ftp, and
pop, the administrator <code class="docutils literal notranslate"><span class="pre">joeadmin</span></code> would issue the command (on
<code class="docutils literal notranslate"><span class="pre">trillium.mit.edu</span></code>):</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">trillium</span><span class="o">%</span> <span class="n">kadmin</span>
<span class="n">kadmin5</span><span class="p">:</span> <span class="n">ktadd</span> <span class="n">host</span><span class="o">/</span><span class="n">trillium</span><span class="o">.</span><span class="n">mit</span><span class="o">.</span><span class="n">edu</span> <span class="n">ftp</span><span class="o">/</span><span class="n">trillium</span><span class="o">.</span><span class="n">mit</span><span class="o">.</span><span class="n">edu</span>
<span class="n">pop</span><span class="o">/</span><span class="n">trillium</span><span class="o">.</span><span class="n">mit</span><span class="o">.</span><span class="n">edu</span>
<span class="n">kadmin</span><span class="p">:</span> <span class="n">Entry</span> <span class="k">for</span> <span class="n">principal</span> <span class="n">host</span><span class="o">/</span><span class="n">trillium</span><span class="o">.</span><span class="n">mit</span><span class="o">.</span><span class="n">edu</span><span class="nd">@ATHENA</span><span class="o">.</span><span class="n">MIT</span><span class="o">.</span><span class="n">EDU</span> <span class="k">with</span>
<span class="n">kvno</span> <span class="mi">3</span><span class="p">,</span> <span class="n">encryption</span> <span class="nb">type</span> <span class="n">DES</span><span class="o">-</span><span class="n">CBC</span><span class="o">-</span><span class="n">CRC</span> <span class="n">added</span> <span class="n">to</span> <span class="n">keytab</span>
<span class="n">FILE</span><span class="p">:</span><span class="o">/</span><span class="n">etc</span><span class="o">/</span><span class="n">krb5</span><span class="o">.</span><span class="n">keytab</span><span class="o">.</span>
<span class="n">kadmin</span><span class="p">:</span> <span class="n">Entry</span> <span class="k">for</span> <span class="n">principal</span> <span class="n">ftp</span><span class="o">/</span><span class="n">trillium</span><span class="o">.</span><span class="n">mit</span><span class="o">.</span><span class="n">edu</span><span class="nd">@ATHENA</span><span class="o">.</span><span class="n">MIT</span><span class="o">.</span><span class="n">EDU</span> <span class="k">with</span>
<span class="n">kvno</span> <span class="mi">3</span><span class="p">,</span> <span class="n">encryption</span> <span class="nb">type</span> <span class="n">DES</span><span class="o">-</span><span class="n">CBC</span><span class="o">-</span><span class="n">CRC</span> <span class="n">added</span> <span class="n">to</span> <span class="n">keytab</span>
<span class="n">FILE</span><span class="p">:</span><span class="o">/</span><span class="n">etc</span><span class="o">/</span><span class="n">krb5</span><span class="o">.</span><span class="n">keytab</span><span class="o">.</span>
<span class="n">kadmin</span><span class="p">:</span> <span class="n">Entry</span> <span class="k">for</span> <span class="n">principal</span> <span class="n">pop</span><span class="o">/</span><span class="n">trillium</span><span class="o">.</span><span class="n">mit</span><span class="o">.</span><span class="n">edu</span><span class="nd">@ATHENA</span><span class="o">.</span><span class="n">MIT</span><span class="o">.</span><span class="n">EDU</span> <span class="k">with</span>
<span class="n">kvno</span> <span class="mi">3</span><span class="p">,</span> <span class="n">encryption</span> <span class="nb">type</span> <span class="n">DES</span><span class="o">-</span><span class="n">CBC</span><span class="o">-</span><span class="n">CRC</span> <span class="n">added</span> <span class="n">to</span> <span class="n">keytab</span>
<span class="n">FILE</span><span class="p">:</span><span class="o">/</span><span class="n">etc</span><span class="o">/</span><span class="n">krb5</span><span class="o">.</span><span class="n">keytab</span><span class="o">.</span>
<span class="n">kadmin5</span><span class="p">:</span> <span class="n">quit</span>
<span class="n">trillium</span><span class="o">%</span>
</pre></div>
</div>
<p>If you generate the keytab file on another host, you need to get a
copy of the keytab file onto the destination host (<code class="docutils literal notranslate"><span class="pre">trillium</span></code>, in
the above example) without sending it unencrypted over the network.</p>
</div>
<div class="section" id="some-advice-about-secure-hosts">
<h2>Some advice about secure hosts<a class="headerlink" href="#some-advice-about-secure-hosts" title="Permalink to this headline">¶</a></h2>
<p>Kerberos V5 can protect your host from certain types of break-ins, but
it is possible to install Kerberos V5 and still leave your host
vulnerable to attack. Obviously an installation guide is not the
place to try to include an exhaustive list of countermeasures for
every possible attack, but it is worth noting some of the larger holes
and how to close them.</p>
<p>We recommend that backups of secure machines exclude the keytab file
(<code class="docutils literal notranslate"><span class="pre">FILE:/etc/krb5.keytab</span></code>). If this is not possible, the backups should at least be
done locally, rather than over a network, and the backup tapes should
be physically secured.</p>
<p>The keytab file and any programs run by root, including the Kerberos
V5 binaries, should be kept on local disk. The keytab file should be
readable only by root.</p>
</div>
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<h2>On this page</h2>
<ul>
<li><a class="reference internal" href="#">UNIX Application Servers</a><ul>
<li><a class="reference internal" href="#the-keytab-file">The keytab file</a></li>
<li><a class="reference internal" href="#some-advice-about-secure-hosts">Some advice about secure hosts</a></li>
</ul>
</li>
</ul>
<br/>
<h2>Table of contents</h2>
<ul class="current">
<li class="toctree-l1"><a class="reference internal" href="../user/index.html">For users</a></li>
<li class="toctree-l1 current"><a class="reference internal" href="index.html">For administrators</a><ul class="current">
<li class="toctree-l2 current"><a class="reference internal" href="install.html">Installation guide</a><ul class="current">
<li class="toctree-l3"><a class="reference internal" href="install_kdc.html">Installing KDCs</a></li>
<li class="toctree-l3"><a class="reference internal" href="install_clients.html">Installing and configuring UNIX client machines</a></li>
<li class="toctree-l3 current"><a class="current reference internal" href="#">UNIX Application Servers</a></li>
</ul>
</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="dbtypes.html">Database types</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>
<li class="toctree-l2"><a class="reference internal" href="appl_servers.html">Application servers</a></li>
<li class="toctree-l2"><a class="reference internal" href="host_config.html">Host configuration</a></li>
<li class="toctree-l2"><a class="reference internal" href="backup_host.html">Backups of secure hosts</a></li>
<li class="toctree-l2"><a class="reference internal" href="pkinit.html">PKINIT configuration</a></li>
<li class="toctree-l2"><a class="reference internal" href="otp.html">OTP Preauthentication</a></li>
<li class="toctree-l2"><a class="reference internal" href="spake.html">SPAKE Preauthentication</a></li>
<li class="toctree-l2"><a class="reference internal" href="dictionary.html">Addressing dictionary attack risks</a></li>
<li class="toctree-l2"><a class="reference internal" href="princ_dns.html">Principal names and DNS</a></li>
<li class="toctree-l2"><a class="reference internal" href="enctypes.html">Encryption types</a></li>
<li class="toctree-l2"><a class="reference internal" href="https.html">HTTPS proxy configuration</a></li>
<li class="toctree-l2"><a class="reference internal" href="auth_indicator.html">Authentication indicators</a></li>
<li class="toctree-l2"><a class="reference internal" href="admin_commands/index.html">Administration programs</a></li>
<li class="toctree-l2"><a class="reference internal" href="../mitK5defaults.html">MIT Kerberos defaults</a></li>
<li class="toctree-l2"><a class="reference internal" href="env_variables.html">Environment variables</a></li>
<li class="toctree-l2"><a class="reference internal" href="troubleshoot.html">Troubleshooting</a></li>
<li class="toctree-l2"><a class="reference internal" href="advanced/index.html">Advanced topics</a></li>
<li class="toctree-l2"><a class="reference internal" href="various_envs.html">Various links</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="../appdev/index.html">For application developers</a></li>
<li class="toctree-l1"><a class="reference internal" href="../plugindev/index.html">For plugin module developers</a></li>
<li class="toctree-l1"><a class="reference internal" href="../build/index.html">Building Kerberos V5</a></li>
<li class="toctree-l1"><a class="reference internal" href="../basic/index.html">Kerberos V5 concepts</a></li>
<li class="toctree-l1"><a class="reference internal" href="../formats/index.html">Protocols and file formats</a></li>
<li class="toctree-l1"><a class="reference internal" href="../mitK5features.html">MIT Kerberos features</a></li>
<li class="toctree-l1"><a class="reference internal" href="../build_this.html">How to build this documentation from the source</a></li>
<li class="toctree-l1"><a class="reference internal" href="../about.html">Contributing to the MIT Kerberos Documentation</a></li>
<li class="toctree-l1"><a class="reference internal" href="../resources.html">Resources</a></li>
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