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Re: Determining the encryption used
From: Peter Kosinar <goober () ksp sk>
Date: Sat, 13 May 2006 15:52:01 +0200 (CEST)

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.

--
[Name] Peter Kosinar   [Quote] 2B | ~2B = exp(i*PI)   [ICQ] 134813278

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