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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Credential cache — MIT Kerberos Documentation</title> <link rel="stylesheet" href="../_static/agogo.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <link rel="stylesheet" href="../_static/kerb.css" type="text/css" /> <script type="text/javascript"> var DOCUMENTATION_OPTIONS = { URL_ROOT: '../', VERSION: '1.15.1', COLLAPSE_INDEX: false, FILE_SUFFIX: '.html', HAS_SOURCE: true }; </script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <link rel="author" title="About these documents" href="../about.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="top" title="MIT Kerberos Documentation" href="../index.html" /> <link rel="up" title="Kerberos V5 concepts" href="index.html" /> <link rel="next" title="keytab" href="keytab_def.html" /> <link rel="prev" title="Kerberos V5 concepts" href="index.html" /> </head> <body> <div class="header-wrapper"> <div class="header"> <h1><a href="../index.html">MIT Kerberos Documentation</a></h1> <div class="rel"> <a href="../index.html" title="Full Table of Contents" accesskey="C">Contents</a> | <a href="index.html" title="Kerberos V5 concepts" accesskey="P">previous</a> | <a href="keytab_def.html" title="keytab" accesskey="N">next</a> | <a href="../genindex.html" title="General Index" accesskey="I">index</a> | <a href="../search.html" title="Enter search criteria" accesskey="S">Search</a> | <a href="mailto:krb5-bugs@mit.edu?subject=Documentation__Credential cache">feedback</a> </div> </div> </div> <div class="content-wrapper"> <div class="content"> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="credential-cache"> <span id="ccache-definition"></span><h1>Credential cache<a class="headerlink" href="#credential-cache" title="Permalink to this headline">¶</a></h1> <p>A credential cache (or “ccache”) holds Kerberos credentials while they remain valid and, generally, while the user’s session lasts, so that authenticating to a service multiple times (e.g., connecting to a web or mail server more than once) doesn’t require contacting the KDC every time.</p> <p>A credential cache usually contains one initial ticket which is obtained using a password or another form of identity verification. If this ticket is a ticket-granting ticket, it can be used to obtain additional credentials without the password. Because the credential cache does not store the password, less long-term damage can be done to the user’s account if the machine is compromised.</p> <p>A credentials cache stores a default client principal name, set when the cache is created. This is the name shown at the top of the <a class="reference internal" href="../user/user_commands/klist.html#klist-1"><em>klist</em></a> <em>-A</em> output.</p> <p>Each normal cache entry includes a service principal name, a client principal name (which, in some ccache types, need not be the same as the default), lifetime information, and flags, along with the credential itself. There are also other entries, indicated by special names, that store additional information.</p> <div class="section" id="ccache-types"> <h2>ccache types<a class="headerlink" href="#ccache-types" title="Permalink to this headline">¶</a></h2> <p>The credential cache interface, like the <a class="reference internal" href="keytab_def.html#keytab-definition"><em>keytab</em></a> and <a class="reference internal" href="rcache_def.html#rcache-definition"><em>replay cache</em></a> interfaces, uses <cite>TYPE:value</cite> strings to indicate the type of credential cache and any associated cache naming data to use.</p> <p>There are several kinds of credentials cache supported in the MIT Kerberos library. Not all are supported on every platform. In most cases, it should be correct to use the default type built into the library.</p> <ol class="arabic"> <li><p class="first"><strong>API</strong> is only implemented on Windows. It communicates with a server process that holds the credentials in memory for the user, rather than writing them to disk.</p> </li> <li><p class="first"><strong>DIR</strong> points to the storage location of the collection of the credential caches in <em>FILE:</em> format. It is most useful when dealing with multiple Kerberos realms and KDCs. For release 1.10 the directory must already exist. In post-1.10 releases the requirement is for parent directory to exist and the current process must have permissions to create the directory if it does not exist. See <a class="reference internal" href="#col-ccache"><em>Collections of caches</em></a> for details. New in release 1.10.</p> </li> <li><p class="first"><strong>FILE</strong> caches are the simplest and most portable. A simple flat file format is used to store one credential after another. This is the default ccache type if no type is specified in a ccache name.</p> </li> <li><p class="first"><strong>KCM</strong> caches work by contacting a daemon process called <tt class="docutils literal"><span class="pre">kcm</span></tt> to perform cache operations. If the cache name is just <tt class="docutils literal"><span class="pre">KCM:</span></tt>, the default cache as determined by the KCM daemon will be used. Newly created caches must generally be named <tt class="docutils literal"><span class="pre">KCM:uid:name</span></tt>, where <em>uid</em> is the effective user ID of the running process.</p> <p>KCM client support is new in release 1.13. A KCM daemon has not yet been implemented in MIT krb5, but the client will interoperate with the KCM daemon implemented by Heimdal. OS X 10.7 and higher provides a KCM daemon as part of the operating system, and the <strong>KCM</strong> cache type is used as the default cache on that platform in a default build.</p> </li> <li><p class="first"><strong>KEYRING</strong> is Linux-specific, and uses the kernel keyring support to store credential data in unswappable kernel memory where only the current user should be able to access it. The following residual forms are supported:</p> <ul class="simple"> <li>KEYRING:name</li> <li>KEYRING:process:name - process keyring</li> <li>KEYRING:thread:name - thread keyring</li> </ul> <p>Starting with release 1.12 the <em>KEYRING</em> type supports collections. The following new residual forms were added:</p> <ul class="simple"> <li>KEYRING:session:name - session keyring</li> <li>KEYRING:user:name - user keyring</li> <li>KEYRING:persistent:uidnumber - persistent per-UID collection. Unlike the user keyring, this collection survives after the user logs out, until the cache credentials expire. This type of ccache requires support from the kernel; otherwise, it will fall back to the user keyring.</li> </ul> <p>See <a class="reference internal" href="#col-ccache"><em>Collections of caches</em></a> for details.</p> </li> <li><p class="first"><strong>MEMORY</strong> caches are for storage of credentials that don’t need to be made available outside of the current process. For example, a memory ccache is used by <a class="reference internal" href="../admin/admin_commands/kadmin_local.html#kadmin-1"><em>kadmin</em></a> to store the administrative ticket used to contact the admin server. Memory ccaches are faster than file ccaches and are automatically destroyed when the process exits.</p> </li> <li><p class="first"><strong>MSLSA</strong> is a Windows-specific cache type that accesses the Windows credential store.</p> </li> </ol> </div> <div class="section" id="collections-of-caches"> <span id="col-ccache"></span><h2>Collections of caches<a class="headerlink" href="#collections-of-caches" title="Permalink to this headline">¶</a></h2> <p>Some credential cache types can support collections of multiple caches. One of the caches in the collection is designated as the <em>primary</em> and will be used when the collection is resolved as a cache. When a collection-enabled cache type is the default cache for a process, applications can search the specified collection for a specific client principal, and GSSAPI applications will automatically select between the caches in the collection based on criteria such as the target service realm.</p> <p>Credential cache collections are new in release 1.10, with support from the <strong>DIR</strong> and <strong>API</strong> ccache types. Starting in release 1.12, collections are also supported by the <strong>KEYRING</strong> ccache type. Collections are supported by the <strong>KCM</strong> ccache type in release 1.13.</p> <div class="section" id="tool-alterations-to-use-cache-collection"> <h3>Tool alterations to use cache collection<a class="headerlink" href="#tool-alterations-to-use-cache-collection" title="Permalink to this headline">¶</a></h3> <ul class="simple"> <li><a class="reference internal" href="../user/user_commands/kdestroy.html#kdestroy-1"><em>kdestroy</em></a> <em>-A</em> will destroy all caches in the collection.</li> <li>If the default cache type supports switching, <a class="reference internal" href="../user/user_commands/kinit.html#kinit-1"><em>kinit</em></a> <em>princname</em> will search the collection for a matching cache and store credentials there, or will store credentials in a new unique cache of the default type if no existing cache for the principal exists. Either way, kinit will switch to the selected cache.</li> <li><a class="reference internal" href="../user/user_commands/klist.html#klist-1"><em>klist</em></a> <em>-l</em> will list the caches in the collection.</li> <li><a class="reference internal" href="../user/user_commands/klist.html#klist-1"><em>klist</em></a> <em>-A</em> will show the content of all caches in the collection.</li> <li><a class="reference internal" href="../user/user_commands/kswitch.html#kswitch-1"><em>kswitch</em></a> <em>-p princname</em> will search the collection for a matching cache and switch to it.</li> <li><a class="reference internal" href="../user/user_commands/kswitch.html#kswitch-1"><em>kswitch</em></a> <em>-c cachename</em> will switch to a specified cache.</li> </ul> </div> </div> <div class="section" id="default-ccache-name"> <h2>Default ccache name<a class="headerlink" href="#default-ccache-name" title="Permalink to this headline">¶</a></h2> <p>The default credential cache name is determined by the following, in descending order of priority:</p> <ol class="arabic simple"> <li>The <strong>KRB5CCNAME</strong> environment variable. For example, <tt class="docutils literal"><span class="pre">KRB5CCNAME=DIR:/mydir/</span></tt>.</li> <li>The <strong>default_ccache_name</strong> profile variable in <a class="reference internal" href="../admin/conf_files/krb5_conf.html#libdefaults"><em>[libdefaults]</em></a>.</li> <li>The hardcoded default, <tt class="docutils literal"><span class="pre">FILE:/tmp/krb5cc_%{uid}</span></tt>.</li> </ol> </div> </div> </div> </div> </div> </div> <div class="sidebar"> <h2>On this page</h2> <ul> <li><a class="reference internal" href="#">Credential cache</a><ul> <li><a class="reference internal" href="#ccache-types">ccache types</a></li> <li><a class="reference internal" href="#collections-of-caches">Collections of caches</a><ul> <li><a class="reference internal" href="#tool-alterations-to-use-cache-collection">Tool alterations to use cache collection</a></li> </ul> </li> <li><a class="reference internal" href="#default-ccache-name">Default ccache name</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"><a class="reference internal" href="../admin/index.html">For administrators</a></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 current"><a class="reference internal" href="index.html">Kerberos V5 concepts</a><ul class="current"> <li class="toctree-l2 current"><a class="current reference internal" href="">Credential cache</a><ul class="simple"> </ul> </li> <li class="toctree-l2"><a class="reference internal" href="keytab_def.html">keytab</a></li> <li class="toctree-l2"><a class="reference internal" href="rcache_def.html">replay cache</a></li> <li class="toctree-l2"><a class="reference internal" href="stash_file_def.html">stash file</a></li> <li class="toctree-l2"><a class="reference internal" href="date_format.html">Supported date and time formats</a></li> </ul> </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> </ul> <br/> <h4><a href="../index.html">Full Table of Contents</a></h4> <h4>Search</h4> <form class="search" action="../search.html" method="get"> <input type="text" name="q" size="18" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <div class="clearer"></div> </div> </div> <div class="footer-wrapper"> <div class="footer" > <div class="right" ><i>Release: 1.15.1</i><br /> © <a href="../copyright.html">Copyright</a> 1985-2017, MIT. </div> <div class="left"> <a href="../index.html" title="Full Table of Contents" >Contents</a> | <a href="index.html" title="Kerberos V5 concepts" >previous</a> | <a href="keytab_def.html" title="keytab" >next</a> | <a href="../genindex.html" title="General Index" >index</a> | <a href="../search.html" title="Enter search criteria" >Search</a> | <a href="mailto:krb5-bugs@mit.edu?subject=Documentation__Credential cache">feedback</a> </div> </div> </div> </body> </html>