M4 Enigma cipher machine, the hardest to crack sold for $437,955 in Christie’s auction


M4 Enigma cipher machine, the hardest to crack sold for $437,955 in Christie’s auction

The Enigma machine is an encryption device developed and used in the early- to mid-20th century to protect commercial, diplomatic, and military communication. It was employed extensively by Nazi Germany during World War II, in all branches of the German military.

Enigma has an electromechanical rotor mechanism that scrambles the 26 letters of the alphabet. In typical use, one person enters text on the Enigma’s keyboard and another person writes down which of 26 lights above the keyboard lights up at each keypress. If plain text is entered, the lit-up letters are the encoded ciphertext. Entering ciphertext transforms it back into readable plaintext. The rotor mechanism changes the electrical connections between the keys and the lights with each keypress.

The design of the M4 is based on the Enigma I, which was already in use at the Wehrmacht (Army and Air Force). It has three moving code wheels, a fixed reflector (UKW), and a Steckerbrett (plugboard), that is located behind a wooden flap at the front.

It was supplied with 8 different coding wheels, (marked I to VIII), three of which were in the machine at any given time. The wiring of wheels I to V was identical to those of the Enigma I. Unlike the Army, however, the Navy choose to have letters (A-Z) on the circumference of each wheel, rather than numbers (01-26).

A rare 1944 four-rotor M4 Enigma cipher machine, considered one of the hardest challenges for the Allies to decrypt, has sold at a Christie’s auction for £347,250 ($437,955). The winning bid for the electromechanical cipher machine was just above the top estimate of £300,000 expected at the auction.

The M4 Enigmas are considered rare because they were made in smaller numbers than three-rotor machines. After Germany capitulated, the country ordered troops to destroy remaining Enigmas in order to keep them from Allied forces. After the war, Winston Churchill also ordered all remaining Enigmas destroyed to help preserve the secret of Allied decoding successes at Bletchley.

The machine’s use of 4 rotors, instead of 3, and the operator’s ability to select these from a pool of 8 interchangeable rotors, together with stricter operating procedures, gave the M4 Enigma a much higher level of encryption.


According to ZDNet, Rival auction house, Sotheby’s sold an M4 Enigma last year for $800,000, which may have reached a higher selling price because it was one of 15 Enigma machines found in a bunker at Germany’s key Northern European naval base in Trondheim, Norway, which Germany had occupied since 1940.


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