From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753692Ab3BUOSM (ORCPT ); Thu, 21 Feb 2013 09:18:12 -0500 Received: from 87-119-183-129.tll.elisa.ee ([87.119.183.129]:37745 "EHLO fatphil.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752297Ab3BUOSJ (ORCPT ); Thu, 21 Feb 2013 09:18:09 -0500 X-Greylist: delayed 440 seconds by postgrey-1.27 at vger.kernel.org; Thu, 21 Feb 2013 09:18:09 EST Date: Thu, 21 Feb 2013 16:07:12 +0200 From: Phil Carmody To: smueller@chronox.de Cc: linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC][PATCH] Entropy generator with 100 kB/s throughput Message-ID: <20130221140712.GA11550@fatphil.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51157686.9000404@chronox.de> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Apologies if this is misthreaded, I had to hand-craft the headers. > The patch offers an entropy generator based on CPU timing jitter. The > entropy collector has the following properties: > > * it does not maintain any state and therefore does not need any seed What is this "pool" if it's not "state"? > /* Entropy pool of the RNG which is filled upon each request for entropy */ > struct rand_data And, from looking at jitterentropy_entropy_calc(), it seems to think that the [source producing the] following sequence of timestamps: 1000, 1010, 1030, 1050, 1060, 1080, 1090, 1110, 1120, ... i.e. with absolutely metronomic deltas of 10, 20, 10, 20, 10, 20, ... has 4 bit of entropy per reading. I hope I don't have to explicitly say that it clearly it has 0 bits of entropy. Entropy harvesting is quite hard - entropy estimation is unimaginably harder. Phil -- "In a world of magnets and miracles" -- Insane Clown Posse, Miracles, 2009. Much derided. "Magnets, how do they work" -- Pink Floyd, High Hopes, 1994. Lauded as lyrical geniuses.