Subject: Re: SHA1 hash safety

From: Tkil <[email-masked]>
Date: Sat, 16 Apr 2005 21:23:37 -0600

>>>>> "Brian" == Brian O'Mahoney <[email-masked]> writes:

Brian> (1) I _have_ seen real-life collisions with MD5, in the context
Brian>     of Document management systems containing ~10^6 ms-WORD
Brian>     documents.

Was this whole-document based, or was it blocked or otherwise chunked?

I'm wondering, because (SFAIK) the MS word on-disk format is some
serialized version of one or more containers, possibly nested.  If
you're blocks are sized so that the first block is the same across
multiple files, this could cause collisions -- but they're the good
kind, that allow us to save disk space, so they're not a problem.

Are you saying that, within 1e7 documents, that you found two
documents with the same MD5 hash yet different contents?

That's not an accusation, btw; I'm just trying to get clarity on the
terminology.  I'm fascinated by the idea of using this sort of
content-addressable filesystem, but the chance of any collision at all
wigs me out.  I look at the probabilities, but still.

Thanks,
t.