Re: Report of collision-generation with MD5

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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