Alice and Bobn. The archetypal individuals used as examples in discussions of cryptographic protocols. Originally, theorists would say something like: "A communicates with someone who claims to be B, So to be sure, A tests that B knows a secret number K. So A sends to B a random number X. B then forms Y by encrypting X under key K and sends Y back to A" Because this sort of thing is is quite hard to follow, theorists stopped using the unadorned letters A and B to represent the main players and started calling them Alice and Bob. So now we say "Alice communicates with someone claiming to be Bob, and to be sure, So Alice tests that Bob knows a secret number K. Alice sends to Bob a random number X. Bob then forms Y by encrypting X under key K and sends Y back to Alice". A whole mythology rapidly grew up around Alice and Bob; see `http://www.conceptlabs.co.uk/alicebob.html'.