From: Nick Kossifidis Subject: Re: [RFC][PATCH] Entropy generator with 100 kB/s throughput Date: Fri, 22 Feb 2013 13:14:14 +0200 Message-ID: References: <51157686.9000404@chronox.de> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: "Ted Ts'o" , linux-crypto@vger.kernel.org, lkml To: Stephan Mueller Return-path: Received: from mail-ve0-f171.google.com ([209.85.128.171]:58371 "EHLO mail-ve0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756026Ab3BVLOP (ORCPT ); Fri, 22 Feb 2013 06:14:15 -0500 In-Reply-To: Sender: linux-crypto-owner@vger.kernel.org List-ID: I'm so sorry, something went terribly wrong with gmail/thunderbird :-( 2013/2/22 Nick Kossifidis : > Hello all, > > It's nice to see there is still discussion on the matter of using cpu > timings for entropy. In general using cpu timings for gathering entropy is a > nice idea but it's not that unpredictable. If someone can profile the system > he/she can get enough infos to predict (to some point) the generator's > outcome, especially during boot/reboot. You might pass the tests on a single > run but if you try to compare the runs e.g. when booting the system multiple > times you'll see they are correlated. > > Take a look at this: > > http://dl.dropbox.com/u/11670313/runtime-data.tar.bz2 > > It's the output of this patch, before passing data to the entropy pool (btw > did anyone review this patch or should I resend it ?): > > https://patchwork.kernel.org/patch/1759821/ > > If you plot the datasets you'll see e.g. that across reboots you get a very > similar distribution. It is somehow different across boots but still there > is some correlation there too, notice the difference when fsck runs, still > not much. > > The distribution is good in general, for mixing it with the rest in the > system's entropy pool, but on its own I don't think it's enough, especially > without crypto post-processing. -- GPG ID: 0xEE878588 As you read this post global entropy rises. Have Fun ;-) Nick