Enigma machine

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Enigma Machine

History of the Enigma

Enigma Basics

The Enigma machine, patented in 1919, displays a keyboard of the twenty-six letters in the pattern of the normal German typewriter, although without numeral or punctuation keys (Stripp 83). It contains three basic parts: “a typewriterlike keyboard on which the plaintext is typed, an internal electromechanical system that converts plaintext to ciphertext, and a display system in which the ciphertext is displayed (Newton 99). The original 1918 Enigma machine contained three rotors, which is the area in charge of transcribing one letter to another and weighed more than one hundred pounds at fifteen inches high. Later editions adopted a more streamline appearance for simpler use and transportation, only weighing fifteen pounds at four inches in height (Newton 100).

Military Necessity

Codebreaking and encryption had not been an essential wartime tactic prior to 1914. However, World War I introduced a necessity for cryptology within the military, especially in regards to commands from high generals and other commanders (Kahn 621).

Pre-WWI Cryptology

During the days of the telegraph and radio, an enemy was capable of intercepting messages sent through the wires or airwaves. When messages were encrypted, breaking the code tended to involve a few brilliant men sitting around a table playing with the cryptogram until a message was configured. The most famous of which occurred during the very beginning of World War I with the Zimmerman Telegraph. The message, from Arthur Zimmermann, the German foreign minister, “proposed that Mexico declare war upon the United States, and that, upon victory, she regain the territories of Texas, New Mexico, and Arizona that she had lost in the Mexican-American War of 1846”. Delivered and published to America, the United States government was able to handle the situation before the Axis Power gained another Ally (Kahn 620). However, this system for cryptanalysis was not the best way to decrypt messages. There was no system for breaking codes, no rulebook or textbook to study in order to simply crack a code. As a result, not all codes could be broken in a timely fashion to be effective.

Post-WWI Cryptology

Most codebreaking occurred in such a fashion throughout the Great War. Battles were won and lost at times based solely on intelligence intercepted and decoded in time to be put to use. World War I demonstrated the importance that cryptology would soon serve in times of battle from then on, including present-day warfare. Even during the time of peace that followed the first World War, “many nations…set up permanent agencies for” cryptanalysis. Many nations had some form of an agency, however, not nearly as large as countries, such as Russia, France, and Italy. Germany, Britain, and America, on the other hand, were the only three major countries to not have such an agency before World War I that developed one soon afterwards. World War I also called for fixing the problem of “error-prone” and “time-consuming” cryptology systems done by hand. When the war was over, many cipher machines were invented and came out onto the market. Most were simple, involving pressing letters on a “typewriter-like keyboard, and the machine would automatically encipher the message.” (Winkel, Deavours, Kahn, Kruh 2). Mechanizing the encryption process made encoding messages, as well as decoding them, faster, more accurately, and more efficiently. Going into World War II, a more complicated cipher machine would be found in Arthur Scherbuius’s Enigma machine.

Enigma Machine: How it Works

What made the Enigma machine so ingenious was, perhaps, its ability to deeply encode messages, almost instantaneously. Encoding a message was no more complicated than simply typing a message on a typewriter (Ratcliff 24). The machine enciphered messages electromagnetically (Ratcliff), and was usually powered by a 4.5 volt battery (Stripp 85). The parts of the machine that were used in the encoding process were the rotors, and a plug board on the front of the machine, called the steckerboard. The steckerboard was a simple plug board which could either be used or unused, or unsteckered. The steckerboard had 26 plugs for each letter, which could be connected by cables to couple certain letters (Stripp 85). Anywhere from 0-13 cables could be used for any given setting, however, usually only 10 cables were used, allowing for the maximum number of permutations for the key (Miller). Additionally, there were three out of five different rotors chosen each day, in a specific order. Each of these five different rotors had a different internal wiring that would move the current in a different manner. Each rotor also had 26 different positions from which the encoded message could begin (Stripp 85).

As each of the different letters of a message was pressed, a current would flow first through the steckerboard. Thus for example if ‘a’ was pressed the current would go to ‘a’ on the steckerboard, where, if the letter was not plugged to another, it would remain the same, or if the letter was plugged to another, the current would flow through, to the new letter (Stripp 85). Next, the current would move through the first rotor, where through the rotor’s internal wiring, it would exit at a different point, or letter, from which it entered. The current would do the same six more times, through the additional two rotors, through the reflector rotor (which was differently wired to ensure the letter would always be encoded and decoded the same way), and back through the three rotors again, lighting up a corresponding, coded, letter on the lamp board. Additionally, after any letter was pressed, the first rotor would turn one step to change the path of the current, so that if ‘a’ were pressed multiple times, it would not yield the same encoded letter. After the first rotor made the full trip around, the second rotor would make one turn, and so on (Ratcliff 15).

Due to this vastly advanced encoding system, the numerical possibilities for the different codes was “astronomical.” Although it was not completely random, the near-randomness of the machine ensured that the usual manners for deciphering codes would be useless against the Enigma (Ratcliff 14-16). It is said that the number of possible combinations was 3 x 10114 (Ratcliff 18). This vast number of various combinations had three different components. First, the steckerboard, which had 0-13 possible connections at a time, to connect different sockets, and connect different letters, each time the machine was set up. Second, was the three rotors, which were chosen and in what order. Finally, was the initial rotational position in which each rotor was set. In each of these combinations, with the rotors turning each time the key was pressed, a key must be pressed 16,900 times before the rotors returned to their original position (Stripp 86). For more on the numerical possibilities in code deviation, see Dr. A. Ray Miller’s “Cryptographic Mathematics of Enigma.”

Each day, the machine would be set up in a different way, which would change the code. The operator would receive orders containing three different essential pieces of information: Which wheels were used and in which order, the ring setting of each of the three wheels, and the steckering. He would then turn the three wheels randomly to a start point. Next, the operator would type out a randomly selected key of three letters, inputted twice, which would give an ‘indicator’ (the letters, as they appeared on the lamp board). He would then set his wheels to the letters typed to yield the lamp board. Each message transmitted would contain the indicator in the beginning to instruct the operator receiving the message in how to set his machine to decipher the message (Stripp 86-87). The receiving operator had his machine set up the same way, as per the daily orders, but he only knew where to start each rotor as per the indicator (Ratcliff 18).

Although the Enigma machine did provide an astronomical number of combinations of codes, there were some limitations. The steckerboard could only connect letters in pairs that denoted the other, thus ‘a’ would be substituted by ‘c’ and vice versa – ‘c’ could not be substituted by anything else in the steckerboard. Additionally, as used by the Nazis, the steckerboard always utilized 10 different connections, not more, and not less. And lastly, the steckers could not link sequential letters, thus ‘a’ could not be linked to ‘b’ and so on. These limitations diminished the number of combinations from 3 x 10114 to 1 x 1023.

Enigma Machine: How it was Used





  • Allsop, F. C. Practical Electric Bell Fitting, a Treatise on the Fitting-up and Maintenance of Electric Bells and All the Necessary Apparatus, with Nearly 150 Illustrations. (London : E & F. N. Spon, 1892).