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<?xml version="1.0" encoding="ascii"?>
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<a href="Crypto-module.html">Package Crypto</a> ::
<a href="Crypto.Hash-module.html">Package Hash</a> ::
Module HMAC
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<!-- ==================== MODULE DESCRIPTION ==================== -->
<h1 class="epydoc">Module HMAC</h1><p class="nomargin-top"></p>
<p>HMAC (Hash-based Message Authentication Code) algorithm</p>
<p>HMAC is a MAC defined in <a class="rst-reference external" href="http://www.ietf.org/rfc/rfc2104.txt" target="_top">RFC2104</a> and <a class="rst-reference external" href="http://csrc.nist.gov/publications/fips/fips198/fips-198a.pdf" target="_top">FIPS-198</a> and constructed using
a cryptograpic hash algorithm.
It is usually named <em>HMAC-X</em>, where <em>X</em> is the hash algorithm; for
instance <em>HMAC-SHA1</em> or <em>HMAC-MD5</em>.</p>
<p>The strength of an HMAC depends on:</p>
<blockquote>
<ul class="rst-simple">
<li>the strength of the hash algorithm</li>
<li>the length and entropy of the secret key</li>
</ul>
</blockquote>
<p>An example of possible usage is the following:</p>
<blockquote>
<pre class="py-doctest">
<span class="py-prompt">>>> </span><span class="py-keyword">from</span> Crypto.Hash <span class="py-keyword">import</span> HMAC
<span class="py-prompt">>>></span>
<span class="py-prompt">>>> </span>secret = b<span class="py-string">'Swordfish'</span>
<span class="py-prompt">>>> </span>h = HMAC.new(secret)
<span class="py-prompt">>>> </span>h.update(b<span class="py-string">'Hello'</span>)
<span class="py-prompt">>>> </span><span class="py-keyword">print</span> h.hexdigest()</pre>
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<span class="summary-type"> </span>
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<a href="Crypto.Hash.HMAC.HMAC-class.html" class="summary-name">HMAC</a><br />
Class that implements HMAC
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<td><span class="summary-sig"><a href="Crypto.Hash.HMAC-module.html#new" class="summary-sig-name">new</a>(<span class="summary-sig-arg">key</span>,
<span class="summary-sig-arg">msg</span>=<span class="summary-sig-default">None</span>,
<span class="summary-sig-arg">digestmod</span>=<span class="summary-sig-default">None</span>)</span><br />
Create a new HMAC object.</td>
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<a name="digest_size"></a><span class="summary-name">digest_size</span> = <code title="None">None</code><br />
The size of the authentication tag produced by the MAC.
It matches the digest size on the underlying
hashing module used.
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<h3 class="epydoc"><span class="sig"><span class="sig-name">new</span>(<span class="sig-arg">key</span>,
<span class="sig-arg">msg</span>=<span class="sig-default">None</span>,
<span class="sig-arg">digestmod</span>=<span class="sig-default">None</span>)</span>
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Create a new HMAC object.
<dl class="fields">
<dt>Parameters:</dt>
<dd><ul class="nomargin-top">
<li><strong class="pname"><code>key</code></strong> (byte string) - key for the MAC object.
It must be long enough to match the expected security level of the
MAC. However, there is no benefit in using keys longer than the
<a href="Crypto.Hash.HMAC-module.html#digest_size" class="link">digest_size</a> of the underlying hash algorithm.</li>
<li><strong class="pname"><code>msg</code></strong> (byte string) - The very first chunk of the message to authenticate.
It is equivalent to an early call to <a href="Crypto.Hash.HMAC.HMAC-class.html#update" class="link">HMAC.update()</a>.
Optional.</li>
<li><strong class="pname"><code>digestmod</code></strong> (A hash module or instantiated object from <a href="Crypto.Hash-module.html" class="link">Crypto.Hash</a>) - The hash to use to implement the HMAC. Default is <a href="Crypto.Hash.MD5-module.html" class="link">Crypto.Hash.MD5</a>.</li>
</ul></dd>
<dt>Returns:</dt>
<dd>An <a href="Crypto.Hash.HMAC.HMAC-class.html" class="link">HMAC</a> object</dd>
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