Date: Tue, 28 Sep 2004 10:15:41 -0500 From: "Jacques A. Vidrine" <nectar@FreeBSD.org> To: Giorgos Keramidas <keramida@linux.gr> Cc: freebsd-security@freebsd.org Subject: Re: compare-by-hash (was Re: sharing /etc/passwd) Message-ID: <20040928151541.GF23453@madman.celabo.org> In-Reply-To: <20040928091405.GB1800@orion.daedalusnetworks.priv> References: <Pine.LNX.4.33.0111071900280.24824-100000@moroni.pp.asu.edu> <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>
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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
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