From: Peter Kosinar (goober@ksp.sk)
Date: Sat May 13 2006 - 09:52:01 EDT
Hello,
> I'm don't know a lot about these matters, but I was under the impression
> that if a password verification system is checking passwords against a
> hash table, all you needed was a collision (as this would hash to the
> correct value in the table and the comparison of the two would return
> true).
Yes and no :-). The question is, what you are trying to achieve. If you
want to be able to replace one file with another one, yet both the files
need to have the same hash, this kind of attack MIGHT help you under some
quite strict conditions (like, you'll most likely need to have control of
both the original and the replacement files).
If, on the other hand, you obtain the password hash and want to find SOME
password corresponding to it, the answer is "no, the known kinds of
weaknesses/attacks will not help you". Neither MD5 nor SHA1 have been
"broken" from this point of view.
Peter
PS. Well, technically, you could set your password to one of the colliding
blocks and use the other one for authentication but I wouldn't consider
this a fatal flaw of the hash.
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