[rc5] Checking for 64 bit RC5 on the fly?

Remi Guyomarch rguyom at mail.dotcom.fr
Mon Jun 23 21:59:56 EDT 1997


Klaus Espenlaub wrote:
> 
> Hi!
> 
> someone please correct me if I'm wrong: The 56 bit keyspace is
> a subspace of the 64 bit one, so the odds of solving the 64bit
> RC5 challenge while doing the current challenge is 1 on 256.
[...]

We are trying to break *one* message, not the cryptosystem. When we will
have the correct key, we will need the same amount of computing power to
break another message encrypted with RC5-56 and 256 times more computing
power to break a message encrypted with RC5-64.

-- 
Rémi
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