re clipper considered harmful restated and amplified in article wcs apr rainier att com wcs anchor ho att com bill stewart writes the serial number will be in a bit block with a bit filler doesn t take a lot to check to see if that is correct depends on whether the filler is a constant makes checking easy but susceptible to replay or variable e g timer counter random which makes replay harder and can also make it easier for the inquisitors to know if they ve missed messages or gotten them out of sequence or other interesting things that sort of person might care about i d use a secret nope obscure cryptographic encoding to expand the bit serial number to a bit block the redundancy hereby introduced can be used to detect tampered clipper signals where some public enemy replaced the l e block by random data and of course the l e block would be used to initialise the encryption of the user data so that at the receiving end the correct l e block must be processed in order to have any chance of getting the plaintext back for those of you who might want to mangle the l e block e g by xor ing a constant pattern on the transmission line and restore it before feeding it into the receiving crippler chip i would add further encrypted copies of this block perhaps created by repeated application of the encryption algorithm or so at regular intervals during the transmission if the receiving chip detects a mismatch it must assume that the line is bad and it will cease to work in your own interest you are protected from getting faulty plaintext you know it s just like a checksum for your own safety the monitoring agencies won t have the famous black box which is needed for actual decryption and will be kept by the fbi but nothing prevents them from using special boxes which will do the redundancy check for the serial number block and consistency checks on the embedded l e blocks within the transmission these boxes will turn a red light on as soon as they detect a bitstream that violates the correct protocol so don t anyone think that you can use the chip and fool l e about the tapping key i bet the developpers have provided much better checks than those suggested above of course it s absolutely crucial that the algorithms and protocols remain secret personally i doubt they will detlef lannert dc ek e mail tsos rz uni duesseldorf de pgp key via server or finger lannert clio rz uni duesseldorf de i am psmith oh you re smith are you with a preliminary p which however is not sounded p g wodehouse
