enigma

Enigma is a family of electro-mechanical rotor cipher machines used to protect military communications in the 20th century. Designed by German engineer Arthur Scherbius, it entered commercial use after World War I and was widely adopted by the German armed forces in the 1930s. Variants and service-specific models followed.

In use, a typist presses a key and electricity passes through a plugboard, rotors, and a reflector before lighting a ciphertext letter. The rotors create a polyalphabetic substitution, and the rightmost rotor steps with each keystroke, changing the wiring for subsequent letters. Daily settings determined the machine's wiring for that day.

There were several versions. Enigma I served the Army and Luftwaffe; the Navy used more capable models, such as the M3 and the later M4, which added a fourth rotor for submarines. Core principles remained the same, but hardware and procedures varied by service.

Security and cryptanalysis: Enigma was considered secure, but weaknesses in procedures and growing cryptanalytic effort allowed Allied readers to intercept many messages. Polish cryptologists led by Marian Rejewski developed early methods and a device called the bomba kryptologiczna before World War II. After Poland's invasion, their work informed Britain and France. At Bletchley Park, Turing, Welchman and colleagues refined methods that produced Ultra intelligence.

Impact: Enigma's reputation for security was challenged by cryptanalysis, and its defeat became a symbol of wartime codebreaking. The collaboration of machines, mathematics, and wartime effort reshaped cryptology and underscored the importance of operational security and procedures as well as device design.