Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S271206AbTHREZm (ORCPT ); Mon, 18 Aug 2003 00:25:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S271210AbTHREZm (ORCPT ); Mon, 18 Aug 2003 00:25:42 -0400 Received: from mailhost.NMT.EDU ([129.138.4.52]:30637 "EHLO mailhost.nmt.edu") by vger.kernel.org with ESMTP id S271206AbTHREZk (ORCPT ); Mon, 18 Aug 2003 00:25:40 -0400 Date: Sun, 17 Aug 2003 22:25:38 -0600 From: Val Henson To: linux-kernel@vger.kernel.org Subject: Re: [RFC][PATCH] Make cryptoapi non-optional? Message-ID: <20030818042538.GA525@speare5-1-14> References: <20030809173329.GU31810@waste.org> <20030815004004.52f94f9a.davem@redhat.com> <20030815095503.C2784@pclin040.win.tue.nl> <20030815202235.GB13384@speare5-1-14> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.1i X-Favorite-Color: Polka dot Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1377 Lines: 35 On Sat, Aug 16, 2003 at 06:27:44AM +0000, David Wagner wrote: > Val Henson wrote: > >If entropy(x) == entropy(y), then: > > > >entropy(x) >= entropy(x xor y) > >entropy(y) >= entropy(x xor y) > > No, that's still wrong. Please see my earlier email with a counterexample. > That counterexample disproves not only the earlier claim, but also this more > recent revised claim. Sigh. Yes, I was thinking of the case where x and y already have maximum entropy, in which case entropy(x) >= entropy(x xor y) For any y. The point I was really trying to make (badly) is that xoring won't increase entropy on average in this particular case (folding the output of SHA-1). In other words, xoring won't make anything better, and has the possibility of making things worse. In any way I evaluate it, folding and truncating are just as good for this particular case, except that folding costs more computationally. (The computational cost was significant enough to have a measurable effect on throughput, so I'm not arm-chair optimizing here.) I sacrifice any earlier points I attempted to make on the altar of hasty mathematics. -VAL - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/