clipper some new thoughts i d desparately prefer it if we didn t rehash the same arguments that went on ad infinitum last time that s especially true for sci crypt for that matter i ve created alt privacy clipper since the traffic is appearing in many different groups right now i m going to focus here on some technical aspects of the plan hence my followup to sci crypt frankly if you re not an absolutist your feelings may turn on some of these issues for example with an bit key simply splitting it into two bit pieces is much less acceptable than other schemes because it means that if just one repository is shall we say overly pliable a would be eavesdropper would need to recover just more bits of key i need not point out in this newsgroup that that s pretty easy to do by exhaustive search a slightly more complex scheme xor ing the key with a random number and then with its complement would produce two bit subkeys neither of which is useful alone that variant is much more resistant to attack clearly one can get even more sophisticated to protect the subkeys even more other thoughts some people have noted the size and complexity of the databases necessary but the id strings the phones emit could be their back door key double encrypted with the escrow repositories public keys for that matter they could do that only with session keys and have no back door at all in that case the fbi would have to bring every intercept to the repositories to be decrypted this would answer many of the objections along the lines of how do you make sure they stop we can even combine that with a variant of the digital telephony back door have the switch do the tap but with a digitally signed record of the time phone number etc of the call that provides proof to the escrow agents that the tap was done in compliance with the terms of the warrant i can suggest other variations too suppose each clipper chip had public key pairs each would be used times after which you d need more keying material not a bad idea in any event this could be used to enforce time limits or rather usage limits on each warrant the keys the repository agents would deliver wouldn t last for very long i suspect that the cryptographic algorithm itself is secure apart from the obvious why push a weak algorithm when you ve already got the back door i think that the government is still genuinely concerned about foreign espionage especially aimed at commercial targets this scheme lets the spooks have their cake and eat it too i ve heard rumors over the years that some factions within nsa were unhappy with des because it was too good not that they couldn t crack it but it was much too expensive to do so as easily as they d want they re keeping the details secret so that others don t build their own implementations without the back door the cryptographic protocol though is another matter i see no valid reasons for keeping it secret and as i hope i ve shown above there are a lot of ways to do things that aren t quite as bad
