I've added some links to my Python-based http://www.inetarena.com/~pdx4d/ocn/clubhouse.html including to an URL where Windows users can download GUI simulators of Enigma machines. The Sale essay on deciphering the Enigma mentions how "no letter my encipher to itself" was actually a weakness of the German system, along with its bidirectionality, i.e. if A enciphered to J, then J enciphered to A. The difference between simple random substitution ala my clubhouse code algorithm (which allows self-substitution) and something like Enigma, is the latter changes the substitution key with each press of a letter (in the Enigma using a complicate system of rotors which, like a car odometer, knocked successive wheels one notch with each complete revolution of the one before). Here's some example plaintext and corresponding ciphertext, from one of the Enigma simulators: Input (note 5-letter chunking): AQUIC KBROW NFOXJ UMPED OVERT HELAZ YDOGW WWWWW WWWWW WWWWW WWWWW WWWWW WWWWW WWWWW WW Output (note how repeated Ws in the input nevertheless enciphers to different letters below): UVWFP ALDFF FMNML SHZLI GTMXM CISQU EIYED FJORN OMNRA CZVXL MRBAO JRGRO ZKCAJ NMMLP AO Also in the news: an Enigma machine stolen from the Bletchy Park museum was recently recovered, along with the internal rotors (found separately, according to newspaper accounts). Another link shows contains some scans of Turing's original typed manuscript re the Enigma, plus there's a virtual tour of Bletchy Park -- all very reinforcing of the storyline developed by Neal Stephenson's 'Cryptonomicon', the novel which originally inspired me to launch this thread. It's be high feasible to write an Enigma simulator in Python of course, including with a GUI front end. But in accordance with my "cave painting" analogy, I think what's important from a pedagogical point of view is, on first pass, to give just the flavor, the essential gist, and then move on to linked topics (e.g. digital circuit design and the evolution of computing hardware). Kirby