Date: Sun, 23 Jul 2000 18:25:34 -0700 (PDT) From: Kris Kennaway <kris@FreeBSD.org> To: "Jeroen C. van Gelderen" <jeroen@vangelderen.org> Cc: Mark Murray <mark@grondar.za>, current@FreeBSD.ORG Subject: Re: randomdev entropy gathering is really weak Message-ID: <Pine.BSF.4.21.0007231809350.79995-100000@freefall.freebsd.org> In-Reply-To: <397B4090.6A15442E@vangelderen.org>
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On Sun, 23 Jul 2000, Jeroen C. van Gelderen wrote:
> > Well, a simple scheme which doesn't seem to suffer from any of the
> > vulnerabilities discussed in the schneier papers is to accumulate entropy
> > in a pool, and only return output when the pool is full. i.e. the PRNG
> > would either block or return 0 bytes of data, or a full pool's worth.
>
> And you can make Yarrow do just that. Not very practical but
> you can do it. You effectively set Pg to 1/(2^(k/3)).
Oh, I missed this - thanks. It does introduce an extra overhead, namely
applying a generator gate with every output (since n < k and Pg < 1) and
then the full reseed with every k bits of output. ITYM Pg = k 2^(-k/3)
though - you want a maximum k bits of output, not 1. I'm not sure if the
current implementation will let you do this (since Pg < 1 here).
> Reseeds do not *have* to happen asynchronously as pointed out
> above.
Yeah, but they do in the current implementation (AFAICT).
Kris
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