On Mon, 13 Jan 1997, Ed Falk wrote:
what do you mean, polyalphabetic substitution?
Someone can correct me if I'm wrong, but I believe it refers to a cipher where each character is encrypted individually, using a different monoalphabetic cipher for each one. The ciphers repeat after a certain period, usually the key length.
Vigenere is the simplest polyalphabetic cipher of them all, with the individual ciphers simply being ROT-n.
I'm convinced that the message in question is a polyalphabetic substitution. Among other things, did people notice quite how much known (or *very easily guessable*) plaintext there was in the message sample, above and beyond the free giveaway of the first line? Things like "CONFIG.SYS", "FILES=20", BUFFERS=20", and so on. There's enough stuff there to make serious inroads into the message without cracking the cipher; and with their help I'm pretty sure the back of the cipher itself can be broken. In the half-hour I played with it I got to the point where I could make some educated guesses about the repetition length of the substitution, and start filling in the various alphabets. No doubt a *real* cryptanalyst could do even better. Alan Bostick | To achieve harmony in bad taste is the height mailto:abostick@netcom.com | of elegance. news:alt.grelb | Jean Genet http://www.alumni.caltech.edu/~abostick