NODE 17d623b2Re: something I've always wondered
wcs@anchor.ho.att.com (bill.stewart@pleasantonca.ncr.com +1-510-484-6204)Wed, 22 Jun 94 10:15:10 PDT
> Jim Miller says:
> > Does DES (or name your favorite encryption algorithm) produce as output
> > all possible cyphertexts of length L, given all possible conbinations of
> > keys and plaintexts of length L?
As Perry points out, for any key, cycling through the 2**64 inputs
will produce all 2**64 outputs. On the other hand, there are
(2**64)! mappings of the set of inputs to the set of outputs,
and DES only uses 2**56 of those mappings, so there are probably
values of P and C for which there is no key K such that C = DES(P,K).