BACKGROUND
Substitution ciphers that encode a message by substituting one
character for another go back at least as far as Julius Caesar, who
used a rotating character scheme to encode military orders. This
simple type of encryption is vulnerable to statistical attacks,
however, as anyone who has solved CRYPTOGRAM puzzles can attest. In
World War II, the Nazi military employed an encryption scheme that
addressed this weakness of simple substitution ciphers. This
scheme, implemented by typewriter-sized devices known as Enigma...