Date: Mon, 17 Jul 2000 12:08:31 -0400 From: "Jeroen C. van Gelderen" <jeroen@vangelderen.org> To: Mark Murray <markm@FreeBSD.ORG> Cc: cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Re: cvs commit: src/sys/sys random.h src/sys/dev/randomdev randomdev.cyarrow.c Message-ID: <39732F7F.2E5BAEC0@vangelderen.org> References: <200007171223.FAA85311@freefall.freebsd.org>
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Mark Murray wrote:
>
> markm 2000/07/17 05:23:04 PDT
>
> Modified files:
> sys/sys random.h
> sys/dev/randomdev randomdev.c yarrow.c
> Log:
> Add randomness write functionality. This does absolutely nothing for
> entropy estimation, but causes an immediate reseed after the input
> (read in sizeof(u_int64_t) chunks) is "harvested".
Arbitrarily reseeding is bad in the case of Yarrow as it
allows for iterative guessing attacks. This is precisely why
this functionality is not described in the paper. Yarrow was
designed to manage the reseeding itself just to prevent this
kind of attack.
You should definately run this kind of input trough the entropy
estimation routines and have Yarrow decide to reseed. You are
writing 4096 bytes anyway (on bootup) so this will (barring
serious bugs) trigger a reseed. If not, you just caught a bug
and the randomness device appears to not work. That's a good
thing.
I'd treat any bytes written to /dev/random as just another
(untrustworthy) entropy source and subject them to a very
conservative (dynamic) entropy estimation.
> This will be used in the reboot "reseeder", coming in another
> commit. This can be used very effectively at any time you think
> your randomness is compromised; something like
>
> # (ps -gauxwww; netstat -an; dmesg; vmstat -c10 1) > /dev/random
>
> will give the attacker something to think about.
If your entropy pool is compromised your attacker has root or
there is a serious bug in Yarrow. In both cases you will want
to take steps to prevent this from happening again...
Cheers,
Jeroen
--
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