Re: Problem with random.c and PPC

From: Andreas Dilger (
Date: Sat Aug 17 2002 - 01:05:07 EST

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

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