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diff --git a/crypto/krb5/doc/html/admin/dictionary.html b/crypto/krb5/doc/html/admin/dictionary.html deleted file mode 100644 index 12ff2f2187ad..000000000000 --- a/crypto/krb5/doc/html/admin/dictionary.html +++ /dev/null @@ -1,224 +0,0 @@ -<!DOCTYPE html> - -<html lang="en" data-content_root="../"> - <head> - <meta charset="utf-8" /> - <meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="viewport" content="width=device-width, initial-scale=1" /> - - <title>Addressing dictionary attack risks — MIT Kerberos Documentation</title> - <link rel="stylesheet" type="text/css" href="../_static/pygments.css?v=fa44fd50" /> - <link rel="stylesheet" type="text/css" href="../_static/agogo.css?v=879f3c71" /> - <link rel="stylesheet" type="text/css" href="../_static/kerb.css?v=6a0b3979" /> - <script src="../_static/documentation_options.js?v=236fef3b"></script> - <script src="../_static/doctools.js?v=888ff710"></script> - <script src="../_static/sphinx_highlight.js?v=dc90522c"></script> - <link rel="author" title="About these documents" href="../about.html" /> - <link rel="index" title="Index" href="../genindex.html" /> - <link rel="search" title="Search" href="../search.html" /> - <link rel="copyright" title="Copyright" href="../copyright.html" /> - <link rel="next" title="Principal names and DNS" href="princ_dns.html" /> - <link rel="prev" title="SPAKE Preauthentication" href="spake.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="spake.html" title="SPAKE Preauthentication" - accesskey="P">previous</a> | - <a href="princ_dns.html" title="Principal names and DNS" - 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__Addressing dictionary attack risks">feedback</a> - </div> - </div> - </div> - - <div class="content-wrapper"> - <div class="content"> - <div class="document"> - - <div class="documentwrapper"> - <div class="bodywrapper"> - <div class="body" role="main"> - - <section id="addressing-dictionary-attack-risks"> -<span id="dictionary"></span><h1>Addressing dictionary attack risks<a class="headerlink" href="#addressing-dictionary-attack-risks" title="Link to this heading">¶</a></h1> -<p>Kerberos initial authentication is normally secured using the client -principal’s long-term key, which for users is generally derived from a -password. Using a pasword-derived long-term key carries the risk of a -dictionary attack, where an attacker tries a sequence of possible -passwords, possibly requiring much less effort than would be required -to try all possible values of the key. Even if <a class="reference internal" href="database.html#policies"><span class="std std-ref">password policy -objects</span></a> are used to force users not to pick trivial -passwords, dictionary attacks can sometimes be successful against a -significant fraction of the users in a realm. Dictionary attacks are -not a concern for principals using random keys.</p> -<p>A dictionary attack may be online or offline. An online dictionary -attack is performed by trying each password in a separate request to -the KDC, and is therefore visible to the KDC and also limited in speed -by the KDC’s processing power and the network capacity between the -client and the KDC. Online dictionary attacks can be mitigated using -<a class="reference internal" href="lockout.html#lockout"><span class="std std-ref">account lockout</span></a>. This measure is not totally -satisfactory, as it makes it easy for an attacker to deny access to a -client principal.</p> -<p>An offline dictionary attack is performed by obtaining a ciphertext -generated using the password-derived key, and trying each password -against the ciphertext. This category of attack is invisible to the -KDC and can be performed much faster than an online attack. The -attack will generally take much longer with more recent encryption -types (particularly the ones based on AES), because those encryption -types use a much more expensive string-to-key function. However, the -best defense is to deny the attacker access to a useful ciphertext. -The required defensive measures depend on the attacker’s level of -network access.</p> -<p>An off-path attacker has no access to packets sent between legitimate -users and the KDC. An off-path attacker could gain access to an -attackable ciphertext either by making an AS request for a client -principal which does not have the <strong>+requires_preauth</strong> flag, or by -making a TGS request (after authenticating as a different user) for a -server principal which does not have the <strong>-allow_svr</strong> flag. To -address off-path attackers, a KDC administrator should set those flags -on principals with password-derived keys:</p> -<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">kadmin</span><span class="p">:</span> <span class="n">add_principal</span> <span class="o">+</span><span class="n">requires_preauth</span> <span class="o">-</span><span class="n">allow_svr</span> <span class="n">princname</span> -</pre></div> -</div> -<p>An attacker with passive network access (one who can monitor packets -sent between legitimate users and the KDC, but cannot change them or -insert their own packets) can gain access to an attackable ciphertext -by observing an authentication by a user using the most common form of -preauthentication, encrypted timestamp. Any of the following methods -can prevent dictionary attacks by attackers with passive network -access:</p> -<ul class="simple"> -<li><p>Enabling <a class="reference internal" href="spake.html#spake"><span class="std std-ref">SPAKE preauthentication</span></a> (added in release -1.17) on the KDC, and ensuring that all clients are able to support -it.</p></li> -<li><p>Using an <a class="reference internal" href="https.html#https"><span class="std std-ref">HTTPS proxy</span></a> for communication with the KDC, -if the attacker cannot monitor communication between the proxy -server and the KDC.</p></li> -<li><p>Using FAST, protecting the initial authentication with either a -random key (such as a host key) or with <a class="reference internal" href="pkinit.html#anonymous-pkinit"><span class="std std-ref">anonymous PKINIT</span></a>.</p></li> -</ul> -<p>An attacker with active network access (one who can inject or modify -packets sent between legitimate users and the KDC) can try to fool the -client software into sending an attackable ciphertext using an -encryption type and salt string of the attacker’s choosing. Any of the -following methods can prevent dictionary attacks by active attackers:</p> -<ul class="simple"> -<li><p>Enabling SPAKE preauthentication and setting the -<strong>disable_encrypted_timestamp</strong> variable to <code class="docutils literal notranslate"><span class="pre">true</span></code> in the -<a class="reference internal" href="conf_files/krb5_conf.html#realms"><span class="std std-ref">[realms]</span></a> subsection of the client configuration.</p></li> -<li><p>Using an HTTPS proxy as described above, configured in the client’s -krb5.conf realm configuration. If <a class="reference internal" href="realm_config.html#kdc-discovery"><span class="std std-ref">KDC discovery</span></a> is used to locate a proxy server, an active -attacker may be able to use DNS spoofing to cause the client to use -a different HTTPS server or to not use HTTPS.</p></li> -<li><p>Using FAST as described above.</p></li> -</ul> -<p>If <a class="reference internal" href="pkinit.html#pkinit"><span class="std std-ref">PKINIT</span></a> or <a class="reference internal" href="otp.html#otp-preauth"><span class="std std-ref">OTP</span></a> are used for -initial authentication, the principal’s long-term keys are not used -and dictionary attacks are usually not a concern.</p> -</section> - - - <div class="clearer"></div> - </div> - </div> - </div> - </div> - <div class="sidebar"> - - <h2>On this page</h2> - <ul> -<li><a class="reference internal" href="#">Addressing dictionary attack risks</a></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"><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="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 current"><a class="current reference internal" href="#">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> -</ul> - 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