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

Klaus Espenlaub kespenla at hydra.informatik.uni-ulm.de
Mon Jun 23 14:40:54 EDT 1997


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.

Would it be worth the time doing another decryption and check
for the other pattern as well? The drawback is obvious: some loss
of speed, but the gain would be the chance to solve the 64 bit RC5
even before the 56 bit RC5 :)

Or did I miss something essential in the RC5 specification? As
far as I understood the algorithm, the words per key stay the
same, thus the key schedule stays the same.

Any comments on this?

Klaus Espenlaub
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