Edit File: hmac.html
<!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>14.2. hmac — Keyed-Hashing for Message Authentication — Python v2.6.6 documentation</title> <link rel="stylesheet" href="../_static/default.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript"> var DOCUMENTATION_OPTIONS = { URL_ROOT: '../', VERSION: '2.6.6', COLLAPSE_MODINDEX: false, FILE_SUFFIX: '.html', HAS_SOURCE: true }; </script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python v2.6.6 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="top" title="Python v2.6.6 documentation" href="../index.html" /> <link rel="up" title="14. 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Cryptographic Services</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="module-hmac"> <h1>14.2. <tt class="xref docutils literal"><span class="pre">hmac</span></tt> — Keyed-Hashing for Message Authentication<a class="headerlink" href="#module-hmac" title="Permalink to this headline">¶</a></h1> <p class="versionadded"> <span class="versionmodified">New in version 2.2.</span></p> <p>This module implements the HMAC algorithm as described by <span class="target" id="index-374"></span><a class="reference external" href="http://tools.ietf.org/html/rfc2104.html"><strong>RFC 2104</strong></a>.</p> <dl class="function"> <dt id="hmac.new"> <tt class="descclassname">hmac.</tt><tt class="descname">new</tt><big>(</big><em>key</em><span class="optional">[</span>, <em>msg</em><span class="optional">[</span>, <em>digestmod</em><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#hmac.new" title="Permalink to this definition">¶</a></dt> <dd><p>Return a new hmac object. If <em>msg</em> is present, the method call <tt class="docutils literal"><span class="pre">update(msg)</span></tt> is made. <em>digestmod</em> is the digest constructor or module for the HMAC object to use. It defaults to the <tt class="xref docutils literal"><span class="pre">hashlib.md5()</span></tt> constructor.</p> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">The md5 hash has known weaknesses but remains the default for backwards compatibility. Choose a better one for your application.</p> </div> </dd></dl> <p>An HMAC object has the following methods:</p> <dl class="method"> <dt id="hmac.hmac.update"> <tt class="descclassname">hmac.</tt><tt class="descname">update</tt><big>(</big><em>msg</em><big>)</big><a class="headerlink" href="#hmac.hmac.update" title="Permalink to this definition">¶</a></dt> <dd>Update the hmac object with the string <em>msg</em>. Repeated calls are equivalent to a single call with the concatenation of all the arguments: <tt class="docutils literal"><span class="pre">m.update(a);</span> <span class="pre">m.update(b)</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">m.update(a</span> <span class="pre">+</span> <span class="pre">b)</span></tt>.</dd></dl> <dl class="method"> <dt id="hmac.hmac.digest"> <tt class="descclassname">hmac.</tt><tt class="descname">digest</tt><big>(</big><big>)</big><a class="headerlink" href="#hmac.hmac.digest" title="Permalink to this definition">¶</a></dt> <dd>Return the digest of the strings passed to the <a title="hmac.hmac.update" class="reference internal" href="#hmac.hmac.update"><tt class="xref docutils literal"><span class="pre">update()</span></tt></a> method so far. This string will be the same length as the <em>digest_size</em> of the digest given to the constructor. It may contain non-ASCII characters, including NUL bytes.</dd></dl> <dl class="method"> <dt id="hmac.hmac.hexdigest"> <tt class="descclassname">hmac.</tt><tt class="descname">hexdigest</tt><big>(</big><big>)</big><a class="headerlink" href="#hmac.hmac.hexdigest" title="Permalink to this definition">¶</a></dt> <dd>Like <a title="hmac.hmac.digest" class="reference internal" href="#hmac.hmac.digest"><tt class="xref docutils literal"><span class="pre">digest()</span></tt></a> except the digest is returned as a string twice the length containing only hexadecimal digits. This may be used to exchange the value safely in email or other non-binary environments.</dd></dl> <dl class="method"> <dt id="hmac.hmac.copy"> <tt class="descclassname">hmac.</tt><tt class="descname">copy</tt><big>(</big><big>)</big><a class="headerlink" href="#hmac.hmac.copy" title="Permalink to this definition">¶</a></dt> <dd>Return a copy (“clone”) of the hmac object. This can be used to efficiently compute the digests of strings that share a common initial substring.</dd></dl> <div class="admonition-see-also admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt>Module <a title="Secure hash and message digest algorithms." class="reference external" href="hashlib.html#module-hashlib"><tt class="xref docutils literal"><span class="pre">hashlib</span></tt></a></dt> <dd>The Python module providing secure hash functions.</dd> </dl> </div> </div> </div> </div> </div> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <h4>Previous topic</h4> <p class="topless"><a href="hashlib.html" title="previous chapter">14.1. <tt class="docutils literal docutils literal docutils literal"><span class="pre">hashlib</span></tt> — Secure hashes and message digests</a></p> <h4>Next topic</h4> <p class="topless"><a href="md5.html" title="next chapter">14.3. <tt class="docutils literal"><span class="pre">md5</span></tt> — MD5 message digest algorithm</a></p> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li><a href="../_sources/library/hmac.txt" rel="nofollow">Show Source</a></li> </ul> <div id="searchbox" style="display: none"> <h3>Quick search</h3> <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> <p class="searchtip" style="font-size: 90%"> Enter search terms or a module, class or function name. </p> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </div> <div class="related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../modindex.html" title="Global Module Index" >modules</a> |</li> <li class="right" > <a href="md5.html" title="14.3. md5 — MD5 message digest algorithm" >next</a> |</li> <li class="right" > <a href="hashlib.html" title="14.1. hashlib — Secure hashes and message digests" >previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="../index.html">Python v2.6.6 documentation</a> »</li> <li><a href="index.html" >The Python Standard Library</a> »</li> <li><a href="crypto.html" >14. 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