winkler@harvard.ARPA (Dan Winkler) (08/21/85)
Sorry to be so devious, but my criminal tendencies inform that it's easy to foil a law against encrypted messages by hiding the encrypted text in what appears to be clear text. Since an encrypted message is simply a string of bits, all you need is a way to hide arbitary bits in a clear text message. One easy way is to hide the bits in a string representing the time. If you write the time as hh:mm:ss using a 24 hour clock, then you have 24 * 60 * 60 = 86,400 permutations. Using the first 64K of those, you can map any 16 bits into what looks like a time of day. Then, all you need to do is find some pretense to send a list of times, such as a list of times you expect to be available for radio contact, and voila, you've transmitted an encrypted message without anyone knowing. Obviously, this little example offers very small throughput, but it's just something I thought up at the keyboard and I'm sure you could do better if you tried. So I think this law only keeps honest people honest and could very well be broken all the time by dishonest people for all we know. I guess that's true of a lot of laws, though. Dan.