The Enigma machine was used by the German military to encode and decode messages during WWII. Allied cryptographers cracked most of the codes, providing important intelligence. The machine was mechanical and had rotating wheels, making it difficult to crack, but patterns in messages and human error helped cryptographers. Primitive computers were used to count possibilities.
The Enigma machine was a mechanical device used to encode and decode secret messages. During World War II, the Enigma machine was used by the German military to communicate with field troops, warships, and submarines. Allied cryptographers, working under the codename ULTRA, successfully cracked most of the Enigma codes; this gave the Allies an important source of intelligence for the war effort.
The Enigma machine itself was mechanical and looked a lot like a typewriter. Each time a key was pressed, the electronic signal passed through a series of spinning shuffle wheels, through a patch panel, and back again in a different direction. Because each wheel could be rotated to alter the signal path, a huge variety of different keystrokes were possible, and the wheels could simply be rotated whenever a new key was needed. The wheels were designed to rotate whenever a key was pressed, making Enigma secure against letter-frequency attacks; the starting positions of the wheels were also changed, often several times a day.
In theory, Enigma was supposed to be secure against any kind of brute force attack, as there were too many encryption possibilities to try them all one by one. Later versions of the Enigma, such as the four-rotor designs used by German U-boats, further increased the number of combinations. Even so, captured coded documents and human error often gave cryptographers the upper hand, and the Polish military was decoding secret German communications as early as 1932. Their work eventually made its way to Britain and America, and cracking of the code continued very successfully throughout the war, despite attempts by the Germans to make the machine more and more complex.
Successfully cracking the Enigma code required finding patterns, or known factors, to reduce the huge number of possible digits. Several simple texts, such as “Heil Hitler”, appeared frequently in German messages; this provided important clues to cryptanalysts, who could search through an encrypted message and see where such a phrase might appear. The Germans also transmitted simple, easy-to-parse six-letter headers at the beginning of messages, such as “EINEIN,” to provide the location of cipher wheels for the rest of the message. When the space of possible code keys still became too large, several primitive computers were built to automatically count the thousands of possibilities; this became one of the earliest jobs done in general purpose computing.
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