Date: Fri, 19 Sep 2003 09:07:05 +0100 From: Mark Murray <markm@freebsd.org> To: "David G. Andersen" <danderse@cs.utah.edu> Cc: freebsd-security@freebsd.org Subject: Re: [Fwd: Re: FreeBSD Security Advisory FreeBSD-SA-03:12.openssh] Message-ID: <200309190807.h8J875fq006577@grimreaper.grondar.org> In-Reply-To: Your message of "Thu, 18 Sep 2003 19:36:36 MDT." <20030918193636.A94860@cs.utah.edu>
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"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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