From owner-freebsd-security@FreeBSD.ORG Tue Sep 28 15:16:06 2004 Return-Path: Delivered-To: freebsd-security@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 7C69516A4CE for ; Tue, 28 Sep 2004 15:16:06 +0000 (GMT) Received: from gw.celabo.org (gw.celabo.org [208.42.49.153]) by mx1.FreeBSD.org (Postfix) with ESMTP id 380B043D49 for ; Tue, 28 Sep 2004 15:16:06 +0000 (GMT) (envelope-from nectar@celabo.org) Received: from localhost (localhost [127.0.0.1]) by gw.celabo.org (Postfix) with ESMTP id A3A625487E; Tue, 28 Sep 2004 10:16:05 -0500 (CDT) Received: from gw.celabo.org ([127.0.0.1]) by localhost (hellblazer.celabo.org [127.0.0.1]) (amavisd-new, port 10024) with SMTP id 20254-04; Tue, 28 Sep 2004 10:15:55 -0500 (CDT) Received: from madman.celabo.org (madman.celabo.org [10.0.1.111]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "madman.celabo.org", Issuer "celabo.org CA" (not verified)) by gw.celabo.org (Postfix) with ESMTP id 0A95354861; Tue, 28 Sep 2004 10:15:55 -0500 (CDT) Received: by madman.celabo.org (Postfix, from userid 1001) id CA24D6D46D; Tue, 28 Sep 2004 10:15:41 -0500 (CDT) Date: Tue, 28 Sep 2004 10:15:41 -0500 From: "Jacques A. Vidrine" To: Giorgos Keramidas Message-ID: <20040928151541.GF23453@madman.celabo.org> Mail-Followup-To: "Jacques A. Vidrine" , Giorgos Keramidas , Jason Stone , freebsd-security@freebsd.org References: <20011107211316.A7830@nomad.lets.net> <20040925140242.GB78219@gothmog.gr> <41575DFC.9020206@wadham.ox.ac.uk> <20040927091710.GC914@orion.daedalusnetworks.priv> <20040927095906.I79820@walter> <20040928091405.GB1800@orion.daedalusnetworks.priv> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20040928091405.GB1800@orion.daedalusnetworks.priv> X-Url: http://www.celabo.org/ User-Agent: Mutt/1.5.6i cc: Jason Stone cc: freebsd-security@freebsd.org Subject: Re: compare-by-hash (was Re: sharing /etc/passwd) X-BeenThere: freebsd-security@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Security issues [members-only posting] List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 28 Sep 2004 15:16:06 -0000 On Tue, Sep 28, 2004 at 12:14:05PM +0300, Giorgos Keramidas wrote: > There is one difference between ``looking for collisions'' and being > bitten by undetected collisions though. > > If the probability of a collision just happening with random user data > is 1/(2^128) we can't be sure that it will necessarily take the > transfer of an average number of 2^127 blocks before a collision > happens. You might get one at the very first pair of blocks and then > no collisions ever after until the Sun burns out. > > Using two different hashes for the same set of input data, which David > G. Andersen proposed, seems like a nice idea though. If you buy the "logic" of the paper, this would not make much difference. After all, composing two hashes just gives you another hash with a longer bit length. This paper needs a lot more peer review, although I'm not sure that many take it seriously enough to bother. Cheers, -- Jacques A Vidrine / NTT/Verio nectar@celabo.org / jvidrine@verio.net / nectar@FreeBSD.org