From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752120Ab3KBLBU (ORCPT ); Sat, 2 Nov 2013 07:01:20 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:42585 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751847Ab3KBLBP (ORCPT ); Sat, 2 Nov 2013 07:01:15 -0400 Date: Sat, 2 Nov 2013 12:01:13 +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: <20131102110112.GA16231@amd.pavel.ucw.cz> References: <2579337.FPgJGgHYdz@tauon> <3160817.9DcncHidey@tauon> <20131029132448.GB691@thunk.org> <7861469.OAmn4h8An0@tauon> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7861469.OAmn4h8An0@tauon> 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 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? For DRAM, just perform timing, have entropy. Plus we could for example measure PIT vs. other timer sources... (but I suspect that on PCs we already have enough entropy...) Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html