From owner-freebsd-security@FreeBSD.ORG  Thu Sep 20 09:20:57 2012
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From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>
To: RW <rwmaillists@googlemail.com>
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Date: Thu, 20 Sep 2012 11:20:56 +0200
In-Reply-To: <20120919231051.4bc5335b@gumby.homeunix.com> (RW's message of
	"Wed, 19 Sep 2012 23:10:51 +0100")
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Cc: freebsd-security@freebsd.org,
	Jonathan Anderson <jonathan.anderson@cl.cam.ac.uk>,
	Pawel Jakub Dawidek <pjd@FreeBSD.org>,
	Mariusz Gromada <mariusz.gromada@gmail.com>
Subject: Re: Collecting entropy from device_attach() times.
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RW <rwmaillists@googlemail.com> writes:
> You're basing a model for all devices on a single sound card, that
> doesn't seem safe to me.  Isn't it possible that a device could take a
> long and well defined time?

Please understand that the timers used here have a resolution of around
1e-8 to 1e-10 seconds.  You may be able to predict the first six digits
with reasonable accuracy - in fact, the first four or five will almost
always be 0, except for devices with moving parts - but anything beyond
that is a crapshoot, even in a virtual machine.

(I am speaking, of course, of decimal digits - multiply by 3.322 for the
corresponding number of bits)

DES
--=20
Dag-Erling Sm=C3=B8rgrav - des@des.no