From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752136Ab3KBLM2 (ORCPT ); Sat, 2 Nov 2013 07:12:28 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:42736 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751876Ab3KBLM0 (ORCPT ); Sat, 2 Nov 2013 07:12:26 -0400 Date: Sat, 2 Nov 2013 12:12:24 +0100 From: Pavel Machek To: Stephan Mueller Cc: "Theodore Ts'o" , sandy harris , linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org Subject: Re: [PATCH] CPU Jitter RNG: inclusion into kernel crypto API and /dev/random Message-ID: <20131102111224.GA19388@amd.pavel.ucw.cz> References: <2579337.FPgJGgHYdz@tauon> <3160817.9DcncHidey@tauon> <20131029132448.GB691@thunk.org> <7861469.OAmn4h8An0@tauon> <20131102110112.GA16231@amd.pavel.ucw.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131102110112.GA16231@amd.pavel.ucw.cz> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat 2013-11-02 12:01:12, Pavel Machek wrote: > Hi! > > > >sense of where the unpredictability might be coming from, and whether > > >the unpredictability is coming from something which is fundamentally > > >arising from something which is chaotic or quantum effect, or just > > >because we don't have a good way of modelling the behavior of the > > >L1/L2 cache (for example) and that is spoofing your entropy estimator. > > > > Please note: if the jitter really comes from the oscillator effect of > > the RAM clock vs. the CPU clock (which I suspect), we will not be able > > to alter the jitter software wise. > > Well... if it is really oscillator effect, there should be _no_ > entropy when running with L1/L2 enabled (because DRAM will not be > accessed at all at that case). > > There should be way to extract entropy more directly from various > oscillator effects, no? Actually... bogomips calibrating loop already has jitter, measured from difference between CPU clock and system clock... Could that be used as entropy source? As a bonus, we should have it on most platforms... Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html