[Fwd: Re: FreeBSD Security Advisory FreeBSD-SA-03:12.openssh]
Mark Murray
markm at freebsd.org
Fri Sep 19 05:28:59 PDT 2003
"David G. Andersen" writes:
> You're mistaken. /dev/random stops feeding you random bits
> when it doesn't have enough. /dev/urandom depletes the entropy
> pool, but when it starts to run out, it falls back to hashing
> to generate pseudo-random sequences from the random bits that
> it can obtain.
Mostly correct :-).
/dev/urandom (in FreeBSD-4-*) always hashes the pool. It doesn't care
whether or not entropy has been harvested first, unlike /dev/random
which requires a positive entropy count before suppying output.
(This provides a doozy of a DoS, BTW, where "cat /dev/urandom > /dev/null"
renders /dev/random useless).
M
--
Mark Murray
iumop ap!sdn w,I idlaH
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