re off the shelf cheap des keyseach machine was re corporate acceptance of the wiretap chip in article apr ulysses att com smb research att com steven bellovin writes in article c sy z td demon co uk graham toal gtoal gtoal com writes in article apr ulysses att com smb research att com steven bellovin writes thousands tens of thousands do some arithmetic please skipjack has possible keys we don t yet know if all bits count that doesn t worry me at all they re not going to cheat at something they can get caught at and key size is one of the things that can be verified externally feed lots of random key input pairs into the chip then try flipping random key bits and see what happens to the output we already know what should happen about half the output bits should vary on average from a bit key change or input change if they were out to build a weak cryptosystem it might be the case that some of the bits are much less powerful than others in the sense that they only enter into the encryption very late in the game by contrast des was designed to use each key bit as early as possible the output change rate appears as early as round again though i don t think nsa is going to cheat that crudely they re likely to get caught consider a cryptosytem that starts out by xoring bits and and not using either of these bits except through this xor this system makes early use of every bit but an exhaustive key search would now only have keys to search your test by varying single key bits wouldn t turn up anything interesting remember that they ve promised to let a committee of outside experts see the cryptosystem design if you assume something des like a biased subkey generation schedule will stick out like a sore thumb the algorithm i suggest above would stick out like a sore thumb but i m sure i could design a system with a more subtle key redundancy which was well hidden but would still make an exhaustive key search take far less than encryptions i don t believe your claim that the real keysize can be verified externally andy latto andyl harlequin com
