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From: Andreas Dilger <adilger@clusterfs.com>
Date: Sat, 17 Aug 2002 00:05:07 -0600
To: Oliver Xymoron <oxymoron@waste.org>
Cc: henrique <henrique@cyclades.com>, linux-kernel@vger.kernel.org
Subject: Re: Problem with random.c and PPC
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On Aug 16, 2002  19:45 -0500, Oliver Xymoron wrote:
> Realistically, the hashing done by /dev/urandom is probably strong
> enough for most purposes. It's as cryptographically strong as whatever
> block cipher you're likely to use with it. /dev/random goes one step
> further and tries to offer something that's theoretically
> unbreakable. Useful for generating things like large public keys, less
> useful for generating the session keys used by SSL and the
> like. They're easier to break by direct attack.

One of the problems, I believe, is that reading from /dev/urandom will
also deplete the entropy pool, just like reading from /dev/random.
The only difference is that when the entropy is gone /dev/random will
stop and /dev/urandom will continue to provide data.

If you are in there fixing things, it might make sense to have
/dev/urandom extract entropy from the random pool far less often than
/dev/random.  This way people who use /dev/urandom for a source of
less-strong randomness (e.g. TCP sequence numbers or whatever), will
not be shooting themselves in the foot for when they need a 2048-byte
PGP key, if they are low on entropy sources.

Cheers, Andreas
--
Andreas Dilger
http://www-mddsp.enel.ucalgary.ca/People/adilger/
http://sourceforge.net/projects/ext2resize/

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