From owner-freebsd-security@FreeBSD.ORG Thu Sep 20 10:03:56 2012 Return-Path: Delivered-To: freebsd-security@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 96024106564A; Thu, 20 Sep 2012 10:03:56 +0000 (UTC) (envelope-from jonathan@FreeBSD.org) Received: from freefall.freebsd.org (freefall.freebsd.org [IPv6:2001:4f8:fff6::28]) by mx1.freebsd.org (Postfix) with ESMTP id 6002C8FC15; Thu, 20 Sep 2012 10:03:56 +0000 (UTC) Received: from [::8037:e412:100:0] (localhost [127.0.0.1]) by freefall.freebsd.org (8.14.5/8.14.5) with ESMTP id q8KA3sSS091406; Thu, 20 Sep 2012 10:03:55 GMT (envelope-from jonathan@FreeBSD.org) Date: Thu, 20 Sep 2012 11:03:55 +0100 From: Jonathan Anderson To: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= Message-ID: In-Reply-To: <86ipb9t5hj.fsf@ds4.des.no> References: <20120918211422.GA1400@garage.freebsd.pl> <20120919192923.GA1416@garage.freebsd.pl> <20120919205331.GE1416@garage.freebsd.pl> <20120919231051.4bc5335b@gumby.homeunix.com> <86ipb9t5hj.fsf@ds4.des.no> X-Mailer: sparrow 1.6.4 (build 1176) MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Cc: freebsd-security@FreeBSD.org, RW , Mariusz Gromada , Pawel Jakub Dawidek Subject: Re: Collecting entropy from device_attach() times. X-BeenThere: freebsd-security@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "Security issues \[members-only posting\]" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 20 Sep 2012 10:03:56 -0000 On Thursday, 20 September 2012 at 10:20, Dag-Erling Sm=C3=B8rgrav wrote: > 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. And this conclusion seems to be borne out by Pawel's data, at least on on= e machine on one architecture. RW's point is still valid, though: if we'r= e going to start asserting that =22we have gathered entropy from source X= =22, we owe it to the consumers of that entropy to really check that we'v= e done what we claim. =46or instance: on an embedded board with few devices, that uses =46DT ra= ther than bus enumeration whatsits, perhaps the time is more deterministi= c and therefore yields less entropy. I don't know, maybe it doesn't, but = we must have data. Jon -- =20 Jonathan Anderson jonathan=40=46reeBSD.org