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<title>15.2 md5 -- MD5 message digest algorithm</title>
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<H1><A NAME="SECTION0017200000000000000000">
15.2 <tt class="module">md5</tt> --
         MD5 message digest algorithm</A>
</H1>

<P>
<A NAME="module-md5"></A>

<P>
This module implements the interface to RSA's MD5 message digest
<a id='l2h-4820' xml:id='l2h-4820'></a>
algorithm (see also Internet <a class="rfc" id='rfcref-92073' xml:id='rfcref-92073'
href="http://www.faqs.org/rfcs/rfc1321.html">RFC 1321</a>).  Its use is quite
straightforward: use <tt class="function">new()</tt> to create an md5 object.
You can now feed this object with arbitrary strings using the
<tt class="method">update()</tt> method, and at any point you can ask it for the
<i class="dfn">digest</i> (a strong kind of 128-bit checksum,
a.k.a. ``fingerprint'') of the concatenation of the strings fed to it
so far using the <tt class="method">digest()</tt> method.
<a id='l2h-4821' xml:id='l2h-4821'></a>

<P>
For example, to obtain the digest of the string <code>'Nobody inspects
the spammish repetition'</code>:

<P>
<div class="verbatim"><pre>
&gt;&gt;&gt; import md5
&gt;&gt;&gt; m = md5.new()
&gt;&gt;&gt; m.update("Nobody inspects")
&gt;&gt;&gt; m.update(" the spammish repetition")
&gt;&gt;&gt; m.digest()
'\xbbd\x9c\x83\xdd\x1e\xa5\xc9\xd9\xde\xc9\xa1\x8d\xf0\xff\xe9'
</pre></div>

<P>
More condensed:

<P>
<div class="verbatim"><pre>
&gt;&gt;&gt; md5.new("Nobody inspects the spammish repetition").digest()
'\xbbd\x9c\x83\xdd\x1e\xa5\xc9\xd9\xde\xc9\xa1\x8d\xf0\xff\xe9'
</pre></div>

<P>
The following values are provided as constants in the module and as
attributes of the md5 objects returned by <tt class="function">new()</tt>:

<P>
<dl><dt><b><tt id='l2h-4813' xml:id='l2h-4813'>digest_size</tt></b></dt>
<dd>
  The size of the resulting digest in bytes.  This is always
  <code>16</code>.
</dd></dl>

<P>
md5 objects support the following methods:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4814' xml:id='l2h-4814' class="function">new</tt></b>(</nobr></td>
  <td><var></var><big>[</big><var>arg</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Return a new md5 object.  If <var>arg</var> is present, the method call
<code>update(<var>arg</var>)</code> is made.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4815' xml:id='l2h-4815' class="function">md5</tt></b>(</nobr></td>
  <td><var></var><big>[</big><var>arg</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
For backward compatibility reasons, this is an alternative name for the
<tt class="function">new()</tt> function.
</dl>

<P>
An md5 object has the following methods:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4816' xml:id='l2h-4816' class="method">update</tt></b>(</nobr></td>
  <td><var>arg</var>)</td></tr></table></dt>
<dd>
Update the md5 object with the string <var>arg</var>.  Repeated calls are
equivalent to a single call with the concatenation of all the
arguments: <code>m.update(a); m.update(b)</code> is equivalent to
<code>m.update(a+b)</code>.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4817' xml:id='l2h-4817' class="method">digest</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Return the digest of the strings passed to the <tt class="method">update()</tt>
method so far.  This is a 16-byte string which may contain
non-ASCII characters, including null bytes.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4818' xml:id='l2h-4818' class="method">hexdigest</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Like <tt class="method">digest()</tt> except the digest is returned as a string of
length 32, containing only hexadecimal digits.  This may
be used to exchange the value safely in email or other non-binary
environments.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4819' xml:id='l2h-4819' class="method">copy</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Return a copy (``clone'') of the md5 object.  This can be used to
efficiently compute the digests of strings that share a common initial
substring.
</dl>

<P>
<div class="seealso">
  <p class="heading">See Also:</p>

  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-sha.html">sha</a></tt>:</b>
    <dd>Similar module implementing the Secure Hash
                  Algorithm (SHA).  The SHA algorithm is considered a
                  more secure hash.
  </dl>
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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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