Re: Avoiding extension attack
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Re: Avoiding extension attack

From: <alexiswarner@gmail.com>
Date: Tue Feb 07 2006 - 18:35:04 CET



Hi Jean,



> Arer you aware that modern hashs use the length to help avoid this?



If you mean the Merkle-Damgaard strenghtening, it can't stop the


extension attack. The adversary calculate the hash of M || L || M' ||


L'


knowing only the hash of M || L (L and L' are the length of M and M' ).


This is why MAC(K, M) = SHA(K || M) is insecure.



> Perhaps you took this in to account, can you please explain all your


> symbols?



What symbol you didn't understand ?


Received on Tue Feb  7 21:00:14 2006