From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932555Ab3KFNZF (ORCPT ); Wed, 6 Nov 2013 08:25:05 -0500 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:43992 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932158Ab3KFNZD (ORCPT ); Wed, 6 Nov 2013 08:25:03 -0500 Date: Wed, 6 Nov 2013 14:24:59 +0100 From: Pavel Machek To: "Theodore Ts'o" , Stephan Mueller , sandy harris , linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, Nicholas Mc Guire Subject: Re: [PATCH] CPU Jitter RNG: inclusion into kernel crypto API and /dev/random Message-ID: <20131106132457.GA13852@amd.pavel.ucw.cz> References: <2579337.FPgJGgHYdz@tauon> <4306229.ErfOL470s2@tauon> <20131106124354.GJ14235@thunk.org> <9172761.DO0L6FkY0c@tauon> <20131106130432.GK14235@thunk.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131106130432.GK14235@thunk.org> 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! > Of course, some of the state in the CPU may not be unknown to the > attacker, if it is derived by external events that are not visible to > the attacker, such as a network interrupt. But if that's the case, > why not measure network interrupts directly? We're much less likely > to overestimate the amount of entropy we can extract the system in > that case. Actually, I believe Stephan is up to something here. We _can't_ measure network interrupts directly, because we do not have TSC. (And TSC-less machines are the ones that are problematic, right?) Extracting entropy from the CPU will allow us to pick up entropy from network packets (and timer interrupt jitter) even on machines that lack TSC. And that counts like very cool feature. (And yes, we could just increment variable to get tsc emulation in idle loop, and then extract entropy from that. But we would not be able to enter low power states at that point, and it would not work when cpu is busy computing.) Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html