Skip site navigation (1)Skip section navigation (2)
Date:      Thu, 20 Sep 2012 11:20:56 +0200
From:      =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>
To:        RW <rwmaillists@googlemail.com>
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.
Message-ID:  <86ipb9t5hj.fsf@ds4.des.no>
In-Reply-To: <20120919231051.4bc5335b@gumby.homeunix.com> (RW's message of "Wed, 19 Sep 2012 23:10:51 %2B0100")
References:  <20120918211422.GA1400@garage.freebsd.pl> <A8FD98DD94774D00B4E5F78D3174C1B4@gmail.com> <20120919192923.GA1416@garage.freebsd.pl> <20120919205331.GE1416@garage.freebsd.pl> <20120919231051.4bc5335b@gumby.homeunix.com>

next in thread | previous in thread | raw e-mail | index | archive | help
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



Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?86ipb9t5hj.fsf>