7DEC98

The Enigma machine, invented by Arthur Scheribus in 1918, was originally for businesses which wanted secure communications. However, with the beginning of World War II, it was in consistent use by the German military.

Before discussing the Enigma machine, it is important to mention basic encoding. The science that deals with encoding messages so that they are not easily read by someone intercepting them is called cryptology. Simple cryptology is the re-mapping of the alphabet such that each letter of the alphabet is represented by another. The simplest form of re-mapping is called one-to-one and is demonstrated here:
 
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However, this sort of message is easily decoded by looking for common letters in the code. By trying logical guesses as to what these letters might be, the code can easily be cracked.

The Enigma machine uses a basic re-mapping scheme, but it goes one step further. The machine is set up with a keyboard, plugboard, rotors, reflector and light board. When the keypad is pressed, the signal first goes to a plugboard where it is exchanged with one other letter. The signal next goes to the rotors. In each rotor, the letter is matched with one other. It then goes to a reflector rotor which sends the signal through the rotors one more time. After passing through the plugboard, the signal illuminates a letter on a light pad. That letter is written down and the next letter is entered.

However, this process is really just a long one-to-one mapping except that the rotors move. The right most rotor, the rotor the signal first passes through, rotates on letter. After each rotor makes one complete rotation, the rotor on its left moves one letter. In essence, this creates a new mapping scheme with each letter. This complex process of changing letters made the code almost unbreakable.

In order for the receiver of an encoded message to read the message, he simply had to set his enigma machine to the same settings that were in place when the message was encoded. This procedure included selecting the three rotors. After setting the index ring on the individual rotor, the wheel was placed on the machines spindle, and the plugboard was set up. The enigma box was then shut, and the wheels were manually set to the starting position. By typing in the encrypted message from beginning to end, the original message would be illuminated.

The mathematical encryption possibilities of the enigma machine are truly staggering. In the simplest machine, each rotor had 26 starting positions which created 17576 (26x26x26) possible mapping for each letter. With six possible ways the rotors could be set in the machine, there was a total of 105456 (17576x6) possibilities for re-mapping. However, this is for just the simplest machines. Improvements were soon made that included five rotors from which three would be selected. The naval version of the machine, used mainly on U-boats, had four rotors in the actual machine. This increased the number of re-mapping possibilities to 3,655,808 (26^4x8).

Although the machine is impressive, it is not completely unbreakable. Daily settings for the machine were given in a code book. This setting was called the ground setting. The operator was then to adjust his rotors to a new setting. After adjusting the setting, the operator sent the same three letters twice in the same order. From this information, the person receiving the message could set up his machine accordingly. However, the Polish code breakers soon picked up on this practice and were able to begin decoding German messages.

Another practice developed for the breaking of the codes was looking for "females." Females occurred when two letters know to be the same due to repetition were enciphered to the same letter. The females for each setting of the machine could be listed, and by observing many messages for the same day, the settings for the day could be determined.

Breaking coded messages was nowhere near as glamorous as history would make it sound. In order to decipher the messages, cryptologists had to consistently discover the daily settings. Most often, this resulted from the German operator making a mistake or the capturing of a German code book. By the end of World War II, Bletchley Park, which was the center of allied message decoding, had more than 10,000 people working around the clock shifts.