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|"Enigma" originates from the Greek and means "mystery" or "riddle".
An almost perfect name for a coding system that became famous for its use during WW II. German military authorities used the Enigma to code secret messages into radio communications. Interestingly, the intensive efforts of the scientists around Alan Turing led to the decoding of the Enigma and also substantially contributed to the development of calculating machines and later to the development of early computers.
The "Enigma" was the first widespread automatic coding and decoding system.
History of cryptography began already several thousand years before the Enigma was built. Coding methods practiced at that time (e.g. use of non-standard hieroglyphics in Egypt, indication substitution with reverse alphabet in Palestine, shifting codes during Caesar's empire) are naturally very simple - compared with our current knowledge. But these coding methods were substantially extended and refined during the course of the centuries.
But only in the 20th centuries rotor machines - like the mentioned Enigma - played a special role not only within the military, but also in crypto-analysis. Rotor machines code by changing gradually their condition based on a set of known parameters. This is comparable with today's pseudo-random number generator. If the initial condition is known, all subsequent conditions are known as well; thus an encoded message can be decoded again.
The invention of Enigma's internal principal goes back to the American building contractor Edward Hugh Hebern (1869 - 1952), who invented in 1917 a rotary device for a polyalphabetic substitution method using independent alphabets. Strangely enough, the American military did not show interest in its machine.
In 1918 German engineer Arthur Scherbius (1878 - 1929) patented the rotor principle and manufactured in its Berlin company "Cipher Machines AG" a rotor machine, which he named "Enigma". He presented Enigma to the public on several congresses and exhibitions in Berne, Stockholm and Leipzig during the early 20's. Enigma was not held secret at all at this time, because Scherbius tried to market it as "equipment for the transmission of business reports and telegrams".
In 1927 Scherbius bought the patents of the Dutch Hugo Alexander Koch, who had invented a more sophisticated rotor principle in 1919. After Scherbius' death technical developing of the Enigma was further led by Willi Korn.
Internationally seen the interest for a governmental use of the machine was almost non existing. Starting in 1926 the German Reichswehr acquired a larger number of Enigmas. During WWII, Enigma was the most common used but not the only coding machine of the Germans. Strategic messages were coded with a few far more complex machines.
Each individual electrical path goes through each of three rollers to a front and a rear contact from there to the so-called turn around wheel (Umkehrwalze) and from there again back through all rollers and additionally the plugs of the patch board. The coding scheme used a quite complicated system: in each roller the adjacent entrance and output contacts are not connected with one another galvanically, but they are meshed against each other after a certain system; the setting on the patch board is varied; with each push of a button the rollers are turning after a certain system one position at a time; out of a set of five only three are selected and used in new order; also the initial setting of the rollers is always newly chosen; at each individual roller a shim is adjusted.
That changed on May 9 1941 when the German submarine U 110 sank. The British soldiers saved an Enigma from the sinking ship complete with the rollers, signal booklet, code sentences and other immensely important documentation. The captured Enigma was still showing some settings that were used on that day and so Bletchley Park was finally able to decode the radiograms and hand them over to the Royal Navy. With this information the Allies could steer evasive courses away from the German submarine fleet. German Admiral Dönitz had to solve a riddle for himself: he could not explain why from one day to the other the calculated quota for each boat, day on sea and sunk tonnage dropped to only 51 tons in January 1943. Despite intensive investigation no explanation could not be found by the Germans. However, each time the German Marine used a more sophisticated Enigma, cryptographers in Bletchley Park encountered a surprising "black out". So e.g. in February of 1942 when a new Enigma with twelve rollers created extended key ranges. Or in 1943 when the German Marine introduced in its Enigma an additional roller and therefore let the scientists at Bletchley Park stand again in the dark for almost 10 months.
After the end of WW II Enigmas were still used in Africa, in the Near East as well as South America. They served in military and diplomatic communication.
With the today's computer technology it might not be difficult to break the Enigma with a plain language attack or brute force attack.