From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760168AbaGRHQR (ORCPT ); Fri, 18 Jul 2014 03:16:17 -0400 Received: from imap.thunk.org ([74.207.234.97]:42529 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755283AbaGRHQO (ORCPT ); Fri, 18 Jul 2014 03:16:14 -0400 Date: Fri, 18 Jul 2014 02:23:56 -0400 From: "Theodore Ts'o" To: "H. Peter Anvin" Cc: Linux Kernel Developers List , linux-crypto@vger.kernel.org, Linus Torvalds Subject: Re: [PATCH] random: limit the contribution of the hw rng to at most half Message-ID: <20140718062356.GC1491@thunk.org> Mail-Followup-To: Theodore Ts'o , "H. Peter Anvin" , Linux Kernel Developers List , linux-crypto@vger.kernel.org, Linus Torvalds References: <1405591436-15445-1-git-send-email-tytso@mit.edu> <53C80A6D.5010201@zytor.com> <20140717220806.GW1491@thunk.org> <53C85D50.5040901@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53C85D50.5040901@zytor.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on imap.thunk.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 17, 2014 at 04:33:36PM -0700, H. Peter Anvin wrote: > > I just want to make sure we don't negatively impact the real security of > users because of "optics". We already have a lot of problems with > people extracting long-living keys from /dev/urandom because /dev/random > is too slow. With a system with RDRAND, we're mixing arch_get_rand_long() as part of the extraction process (as the seed for the SHA's IV). So if you trust RDRAND, then using /dev/urandom even when the entropy count is zero is going to be secure. If you don't trust RDRAND, then the RDSEED entropy accounting is going to be extremely disturbing. So the only way that we could be impacting the "real security" of users, would be if RDRAND was back-doored, but RDSEED wasn't. And that doesn't seem like a terribly likely scenario to me, but what do I know? :-) - Ted