In reference to a message by Mike Johnson: I was thinking of steganography as being in two stages: first, you encrypt, (possibly with the identity transformation) then, you embed your encrypted message in your medium of transmission. My previous message was describing requirements for a strong encryption algorithm, quite apart from the actual embedding. I stand by my statements: the purpose of steganography is to make it difficult or impossible for an interloper to determine that enciphered data are being transferred. Thus, embedding a magic number in the file defeats the purpose completely. (As opposed to "slightly reducing security.") I accept your correction regarding availability of software. I think that designing a program to embed this apparently random bitstream in an innocent-looking file is a different and much harder problem. It is probable that I have misunderstood some part of your message, and I apologize if this is the case. Kragen (Bug my sysman for a newsreader that allows quoting with >'s-his username is jim.)