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Date: Tue, 11 Jul 2006 15:50:38 -0400
From: Chuck Swiger <cswiger@mac.com>
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To: Mike Tancsa <mike@sentex.net>
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Cc: freebsd-security@freebsd.org
Subject: Re: Integrity checking NANOBSD images
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Mike Tancsa wrote:
[ ... ]
> # ssh remote1.example.com "/tmp/rand-directory/dd if=/dev/ad2s1a 
> bs=4096k | /tmp/rand-directory/sha256"
> 120+1 records in
> 120+1 records out
> 505389056 bytes transferred in 169.727727 secs (2977646 bytes/sec)
> 955ebad583bfc0718eb28ac89563941407294d5c61a0c0f35e3773f029cc0685
> 
> Can I be reasonably certain the image has not been tampered with ?  Or 
> are there trivial ways to defeat this check ?

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.

-- 
-Chuck