From: Nikos Mavrogiannopoulos Subject: Re: [PATCH] random: add blocking facility to urandom Date: Wed, 07 Sep 2011 23:20:48 +0200 Message-ID: <4E67E030.1020702@gmail.com> References: <1314974248-1511-1-git-send-email-jarod@redhat.com> <4E67B75B.8010500@redhat.com> <20110907192737.GD20571@thunk.org> <201109071602.24519.sgrubb@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Ted Ts'o , Jarod Wilson , Sasha Levin , linux-crypto@vger.kernel.org, Matt Mackall , Neil Horman , Herbert Xu , Stephan Mueller , lkml To: Steve Grubb Return-path: Received: from mail-ww0-f44.google.com ([74.125.82.44]:65316 "EHLO mail-ww0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754554Ab1IGVUh (ORCPT ); Wed, 7 Sep 2011 17:20:37 -0400 In-Reply-To: <201109071602.24519.sgrubb@redhat.com> Sender: linux-crypto-owner@vger.kernel.org List-ID: On 09/07/2011 10:02 PM, Steve Grubb wrote: > When a system is underattack, do you really want to be using a PRNG > for anything like seeding openssl? Because a PRNG is what urandom > degrades into when its attacked. Using a PRNG is not a problem. Making sure it is well seeded and no input from the attacker can compromise its state are the difficult parts. Making predictable estimates and blocking when your estimates are off, makes it a good target for DoS. When your system is under attack, you want to use your services. If they block then the attack might have just been successful. regards, Nikos