Spy and Terrorist Briefing Center

Enigma: The Best Known Cipher Machine in the World

Enigma was the name of the infamous cipher machine used by the Nazis in World War II. It was a very complex system for its time and its encryption went unbroken for almost fifteen years.

As you can see from the picture, the machine is contained in a wooden box small enough for a single person to carry. Inside the box is a typewriter-like arrangement. Above the typewriter is an array of lamps, one lamp for each letter. When a key is pressed, a lamp is illuminated. The lamp indicates the enciphered letter. Typically, two operators were used to code a message. One operator typed the message, while the second read the encrypted one from the lamps.

The encryption was accomplished via three rotors located above the lamps. The rotors were the key to the system. When a letter was typed and the system activated, the letter was fed into the first rotor, where a new letter would emerge. The new letter fed into the second rotor, spitting out a different letter. This new letter was fed into the third rotor, which gave a different letter. This new letter would then enter a reflector, which operated like a rotor, but without the rotational capabilities. After the reflector, it went back through each of the rotors in the reverse order it initially passed through. Here's a diagram of how it might work if there were only eight letters in the alphabet. To make matters worse, each of the rotors turned at different rates. The key effect of this feature was that the letter "A" might be ciphered into a "W" in one part of the message and be an "F" in another part. In all, there would be approximately 1.2 sextillion possible keys to any message. That would be 1,200,000,000,000,000,000,000 possibilities!!! Computers did not exist in those days, and that number was too big to try to go through all of them manually.

In order to decipher a message, the machine is reset to exactly the same position and the enciphered message is typed in (this would normally be done on a distant machine). The original message now appears on the lamps. The Enigma machine is 'symmetrical,' meaning the enciphering and deciphering method is the same, but the machines must be identically set up. In order for the recipient to decode the message, they would need to know the initial settings of the rotors, and then put the cipher text through the machine to find the plain text. The Germans devised a system by which all of the recipients would set their rotors to predetermined settings according to the date. Each clerk had a book detailing the settings for each day. This presented a major weakness in the system. Obviously, if anyone could figure out what the settings of the rotors were for a particular day, they would be able to decode that day's messages, assuming they had an Enigma Machine themselves.

Three Polish scientists made the first inroads into breaking the cipher. Marian Rejewski, Jerzy Rozycki, and Henryk Zygalskiis worked at the Polish Cipher Bureau in the early 1930s. He began working on breaking the Enigma cipher in 1933 and continued until Poland was invaded by the Nazis in 1939. At that point, the Polish turned over their work to the British, where a Cambridge- and Princeton-educated mathematician named Alan Turing led the team that broke the cipher in 1942.

The breaking of this cipher led to the Allies' ability to intercept and decode the Germans' messages. The Germans never believed that the Enigma messages could be deciphered and continued to use it until the end of the war. The Enigma cipher was so powerful, some speculate that the war might have turned out much differently had it not been broken.

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