WWII German Enigma Code Machine

Recently I read a fascinating book: Enigma, the Battle for the Code, by Hugh Sebag-Montefiore. It’s about breaking the German Enigma military code from WWII by the joint, but not always cooperative, effort of the Polish, British and American code breakers. The author has had access to recently released secret documents from the 1940’s and so was able to tell the story in a lot more detail than was previously possible.

The code was a combination of constantly changing settings and a series of machines used by the German military during the war to send and receive encrypted radio traffic. This model is based on the naval Enigma machine used by the Kriegsmarine , most significantly by the U-boats in the Atlantic and the Northern passage between Iceland and the USSR.

The machines used codes and settings based on instructions which varied from time-to-time. When a key was depressed, an electric current was passed through the plug board on the front of the machine and then through a series of wheels in the rear which were wired to scramble the current connections in millions of different ways. Each wheel could be turned to 26 different positions and the positions of the individual wheels could be rearranged. The arrangement of the plug board and the position and rotation of the wheels were given out to the boats on paper. The resulting ciphered letter was shown on the lighted round windows above the keyboard. As each key was pressed, the telegrapher noted down the corresponding cipher on his pad. When the message was complete, the coded version was sent in Morse code.

Curiously, an early commercial version of the Enigma machine was awarded a United States patent in 1928.