Date: Tue, 11 Jul 2006 16:24:07 -0400 From: Chuck Swiger <cswiger@mac.com> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: freebsd-security@freebsd.org Subject: Re: Integrity checking NANOBSD images Message-ID: <44B408E7.8070000@mac.com> In-Reply-To: <77121.1152648353@critter.freebsd.dk> References: <77121.1152648353@critter.freebsd.dk>
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Poul-Henning Kamp wrote: > In message <44B4010E.7010809@mac.com>, Chuck Swiger writes: >> Checksumming the device image is a fine way of checking the integrity of it, >> assuming it is read-only. The only thing you might want to do is use two or >> three checksum algorithms (ie, use sha256 and md5 and something else), so that >> someone can't create a new image which matches the sha256 checksum of the >> original. > > A much better idea is to send a random "salt" to be prepended to > the disk image before it is run through sha256, that would prevent > the attacker from running sha256 and any other algorithm you > could care for on the image, store the results and return them > with trojans. That suggestion is a very good point, although trying to find a single trojaned image which matches several checksum methods is supposed to be a highly difficult task. -- -Chuck
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