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<div class="section" id="module-hmac">
<span id="hmac-keyed-hashing-for-message-authentication"></span><h1>14.2. <a class="reference internal" href="#module-hmac" title="hmac: Keyed-Hashing for Message Authentication (HMAC) implementation for Python."><tt class="xref py py-mod docutils literal"><span class="pre">hmac</span></tt></a> — Keyed-Hashing for Message Authentication<a class="headerlink" href="#module-hmac" title="Permalink to this headline">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="http://hg.python.org/cpython/file/3.2/Lib/hmac.py">Lib/hmac.py</a></p>
<hr class="docutils" />
<p>This module implements the HMAC algorithm as described by <span class="target" id="index-0"></span><a class="rfc 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>, <em>msg=None</em>, <em>digestmod=None</em><big>)</big><a class="headerlink" href="#hmac.new" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a new hmac object. <em>key</em> is a bytes object giving the secret key. 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 py py-func docutils literal"><span class="pre">hashlib.md5()</span></tt> constructor.</p>
</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><p>Update the hmac object with the bytes object <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>.</p>
</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><p>Return the digest of the bytes passed to the <a class="reference internal" href="#hmac.hmac.update" title="hmac.hmac.update"><tt class="xref py py-meth docutils literal"><span class="pre">update()</span></tt></a> method so far.
This bytes object will be the same length as the <em>digest_size</em> of the digest
given to the constructor. It may contain non-ASCII bytes, including NUL
bytes.</p>
</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><p>Like <a class="reference internal" href="#hmac.hmac.digest" title="hmac.hmac.digest"><tt class="xref py py-meth 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.</p>
</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><p>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.</p>
</dd></dl>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt>Module <a class="reference internal" href="hashlib.html#module-hashlib" title="hashlib: Secure hash and message digest algorithms."><tt class="xref py py-mod docutils literal"><span class="pre">hashlib</span></tt></a></dt>
<dd>The Python module providing secure hash functions.</dd>
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