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To: "Devon H. O'Dell" <dodell@sitetronics.com>
From: Mark Murray <markm@freebsd.org>
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cc: freebsd-security@freebsd.org
Subject: Re: [Fwd: Re: FreeBSD Security Advisory FreeBSD-SA-03:12.openssh] 
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"Devon H. O'Dell" writes:
> If I'm not mistaken, /dev/random is a pseudo-random generator, which 
> means it has a certain period before it begins to repeat numbers (along 
> with that it just isn't truly random). So, please correct me if I'm 
> wrong, but doesn't this mean that when reading from /dev/random, you're 
> 'losing' randomness/entropy/whatever you're calling it?

You are very mistaken indeed :-).

In FreeBSD-4-*, /dev/random is an "entropy distiller", albeit not a very
good one as it is not very conservative. On that system, /dev/urandom is
a very complex PRNG, with the added feature of being perturbed by actual
entropy.

In FreeBSD-5-* there is no separate /dev/urandom, and /dev/random is 
driven by Yarrow (http://www.counterpane.com/yarrow/). This is a
PRNG+entropy-harvester, and it it _very_ conservative. As long as
_some_ entropy is being harvested, it is unlikely that either generator
wil produce a repeating sequence _ever_.

M
--
Mark Murray
iumop ap!sdn w,I idlaH