Date: Sat, 26 Dec 2009 03:32:16 +0000 From: RW <rwmaillists@googlemail.com> To: freebsd-hackers@freebsd.org Subject: Re: yarrow random generator Message-ID: <20091226033216.145bb35f@gumby.homeunix.com> In-Reply-To: <4B3530C2.4020607@FreeBSD.org> References: <5a5b03660912240445x7df1498dt42e29d93105efebc@mail.gmail.com> <oCmohG1K70vWpt/39IVPMdciTgk@DNdB9ElzNmEFYWRqT2UTVtuts%2BE> <4B339F27.6020707@freebsd.org> <5a5b03660912240941r6b76a839u819a8a1408816386@mail.gmail.com> <alpine.BSF.2.00.0912241945490.73550@fledge.watson.org> <20091224231334.2e242371@gumby.homeunix.com> <alpine.BSF.2.00.0912251345230.73550@fledge.watson.org> <4B3530C2.4020607@FreeBSD.org>
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On Fri, 25 Dec 2009 13:38:10 -0800
Doug Barton <dougb@FreeBSD.org> wrote:
> Robert Watson wrote:
> > I'll point Mark Murray at this thread and see if we can get him to
> > opine some on the current design choices and any potential changes
> > to address them. I was interested by your observation that the
> > boot-time dumping of bits into /dev/random may overflow the
> > buffering --
>
> I was peripherally involved in the introduction of yarrow in the sense
> that I wrote most of the rc and periodic stuff for it so I am also
> interested in this issue. Rather than speculating about whether it's
> overflowing the buffer perhaps a patch can be produced to test this
> hypothesis?
It's not really speculation, the data is broken into 16 byte chunks,
random_harvest_internal() is called to copy each chunk into a buffer
and queue it. If there are 256 or more buffers in the queue
random_harvest_internal() returns without doing anything.
The kernel thread that processes the queues calls
pause("-", hz /10) each time it loops.
A fairly simple solution would be piping all that low-grade entropy
from sysctl and ps etc through sha256, reducing it to 64 bytes.
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