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<H2><A NAME="SECTION000420000000000000000"> </A>
<BR>
3.2 <tt class="module">rand</tt> -- An interface to the OpenSSL pseudo random number generator
</H2>
<P>
<P>
This module handles the OpenSSL pseudo random number generator (PRNG) and
declares the following:
<P>
<dl><dt><b><a name='l2h-118'><tt class='function'>add</tt></a></b>(<var>string, entropy</var>)
<dd>
Mix bytes from <var>string</var> into the PRNG state. The <var>entropy</var> argument is
(the lower bound of) an estimate of how much randomness is contained in
<var>string</var>, measured in bytes. For more information, see e.g. <a class="rfc" name="rfcref-2374"
href="http://www.ietf.org/rfc/rfc1750.txt">RFC 1750</a>.
</dl>
<P>
<dl><dt><b><a name='l2h-119'><tt class='function'>bytes</tt></a></b>(<var>num_bytes</var>)
<dd>
Get some random bytes from the PRNG as a string.
<P>
This is a wrapper for the C function <tt class="function">RAND_bytes</tt>.
</dl>
<P>
<dl><dt><b><a name='l2h-120'><tt class='function'>cleanup</tt></a></b>()
<dd>
Erase the memory used by the PRNG.
<P>
This is a wrapper for the C function <tt class="function">RAND_cleanup</tt>.
</dl>
<P>
<dl><dt><b><a name='l2h-121'><tt class='function'>egd</tt></a></b>(<var>path</var><big>[</big><var>, bytes</var><big>]</big>)
<dd>
Query the Entropy Gathering Daemon<A NAME="tex2html2"
HREF="#foot1272"><SUP>2</SUP></A> on socket <var>path</var> for <var>bytes</var>
bytes of random data and and uses <tt class="function">add</tt> to seed the PRNG. The default
value of <var>bytes</var> is 255.
</dl>
<P>
<dl><dt><b><a name='l2h-122'><tt class='function'>load_file</tt></a></b>(<var>path</var><big>[</big><var>, bytes</var><big>]</big>)
<dd>
Read <var>bytes</var> bytes (or all of it, if <var>bytes</var> is negative) of data from
the file <var>path</var> to seed the PRNG. The default value of <var>bytes</var> is -1.
</dl>
<P>
<dl><dt><b><a name='l2h-123'><tt class='function'>screen</tt></a></b>()
<dd>
Add the current contents of the screen to the PRNG state.
Availability: Windows.
</dl>
<P>
<dl><dt><b><a name='l2h-124'><tt class='function'>seed</tt></a></b>(<var>string</var>)
<dd>
This is equivalent to calling <tt class="function">add</tt> with <var>entropy</var> as the length
of the string.
</dl>
<P>
<dl><dt><b><a name='l2h-125'><tt class='function'>status</tt></a></b>()
<dd>
Returns true if the PRNG has been seeded with enough data, and false otherwise.
</dl>
<P>
<dl><dt><b><a name='l2h-126'><tt class='function'>write_file</tt></a></b>(<var>path</var>)
<dd>
Write a number of random bytes (currently 1024) to the file <var>path</var>. This
file can then be used with <tt class="function">load_file</tt> to seed the PRNG again.
</dl>
<P>
<dl><dt><b>exception <a name='l2h-127'><tt class='exception'>Error</tt></a></b>
<dd>
If the current RAND method supports any errors, this is raised when needed.
The default method does not raise this when the entropy pool is depleted.
<P>
Whenever this exception is raised directly, it has a list of error messages
from the OpenSSL error queue, where each item is a tuple <code>(<var>lib</var>,
<var>function</var>, <var>reason</var>)</code>. Here <var>lib</var>, <var>function</var> and <var>reason</var>
are all strings, describing where and what the problem is. See <span class='manpage'><i>err</i>(3)</span>
for more information.
</dl>
<P>
<BR><HR><H4>Footnotes</H4>
<DL>
<DT><A NAME="foot1272">... Daemon</A><A
href="openssl-rand.html#tex2html2"><SUP>2</SUP></A></DT>
<DD>See
<a class="url" href="http://www.lothar.com/tech/crypto/">http://www.lothar.com/tech/crypto/</a>
</DD>
</DL>
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