In
cryptography, a
rotor machine is an electro-mechanical
stream cipher device used for
encrypting and decrypting secret messages. Rotor machines were the cryptographic state-of-the-art for a prominent period of history; they were in widespread use in the 1920s–1970s. The most famous example is the
German Enigma machine, whose messages were deciphered by the Allies during World War II, producing intelligence code-named
Ultra.