Date: Thu, 26 Aug 2004 18:08:11 +1000 From: Peter Jeremy <PeterJeremy@optushome.com.au> To: Brooks Davis <brooks@one-eyed-alien.net> Cc: freebsd-security@freebsd.org Subject: Re: Report of collision-generation with MD5 Message-ID: <20040826080811.GQ423@cirb503493.alcatel.com.au> In-Reply-To: <20040825201640.GB25259@odin.ac.hmc.edu> References: <6.1.2.0.0.20040818141732.04a6e060@64.7.153.2> <XFMail.20040825215150.guy@device.dyndns.org> <20040825201640.GB25259@odin.ac.hmc.edu>
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On Wed, 2004-Aug-25 13:16:40 -0700, Brooks Davis wrote: >On Wed, Aug 25, 2004 at 09:51:50PM +0200, guy@device.dyndns.org wrote: >> I _believe_ answer is "no", because i _think_ the FreeBSD ports system also >> verify the size of the archive(s) (cat /usr/ports/any/any/distinfo to see >> what made me think that). I don't believe the size adds much security. >Paranoia might suggest adding support for multiple hashes which would >vastly increase the difficulty of finding a collision I'd agree with this. Identifying suitable hashes is a more difficult task. >Hmm, one thing to think about might be making sure the various archive >formats are hard to pad with junk. I think the stream based ones need >to allow zero pading at the end to support tapes, but it would be >intresting to see if other junk can end up in pading sections without >the archiver noticing. If so, that would be a good thing to find a way >to detect. tar uses one (or two) blocks of NULs to mark logical EOF - anything beyond that is ignored. gzip ignores (but warns) about padding after its expected EOF. I'm not sure about bzip2. I suspect it would be possibly to include arbitrary padding inside a ZIP file, though probably not at the end. This would make it relatively easy to pad a trojan'd file to any desired size. -- Peter Jeremy
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