The Enigma Machine

Discussion in 'General Discussion' started by melbo, Jan 24, 2006.

  1. melbo

    melbo Hunter Gatherer Administrator Founding Member


    The German Enigma is surely the best known of the WW2 cipher machines used by either side in the conflict. Invented in 1918, it was developed as both a commercial and military encipherment system before and during the war. Enigma is an electro-mechanical device that utilizes a stepping wheel system to 'scramble' a plaintext message to produce ciphertext via polyalphabetic substitution. Potentially, the number of ciphertext alphabets is astronomically large - a fact that led the German military authorities to believe, wrongly as it turned out, in the absolute security of this cipher system.

    Enigma - principle:
    Enigma's output is a very complex polyalphabetic substitution ciphertext. The 3-wheel Service Enigma consists of a number of components. A message to be enciphered is input from a keyboard - QWERTZUIO layout. The signal leaves the keyboard and passes through a plugboard where, if the plugboard socket contains a connector, its identity is switched in a monoalphabetic substitution. If the particular socket does not contain a plug, the identity of the input character is unchanged. The plugboard substitution is reciprocal - i.e. if A is switched to Z, then Z is switched to A, a weakness that was to be exploited by Allied cryptanalysts.

    From the plugboard the signal then passes to the entry stator which passes it to the first of a series of three wheels. Each of these has twenty-six contacts on each of its faces, cross-wired in a random fashion so that the identity of an incoming character is changed three times as it passes through the three wheels, which are in electrical contact, each with its adjacent companion. With each keyboard input the extreme right-hand wheel moves one position - before encipherment takes place. Additionally, once during a complete revolution of each wheel, the wheel to its left steps once.

    After passing through all three wheels the signal reaches the reflector which performs two functions - it changes the signal's identity once again and also sends it back, in the reverse direction, through the three wheels to the entry stator. From here it passes back to the plugboard and then to the lampboard where a lamp corresponding to the now enciphered character is illuminated.

    Because of the reflector's function in the encipherment process, no plaintext character can ever encipher to itself - another weakness in the system that was exploited to great effect by the Allied cryptanalysts.

    Enigma was set up according to whatever procedural instructions prevailed at the time by adjusting the following parameters.

    Walzenlage: Three wheels were selected from a set of five in the case of the Army and Air Force machines - from a set of eight in the case of the Naval machines. The daily [or other periodic] instructions would also specify the reflector [Umkehrwalze] and, in the case of the Kriegmarine's M4, the selection of the fourth, 'Greek' , wheel and its 'thin' reflector.

    Ringstellung: After setting the index ring on each, the three wheels were arranged on the machine's spindle in the order prescribed in the daily [or other periodic] instructions for machine initialization.

    Steckers: The plugboard was set up according to the same instructions. Normally, ten sets of plugs were used leaving six letters 'self-steckered'.

    The internal lid of the Enigma was closed and the wheels set to the initial position.

    Enigma was then ready for use.

    You can download a working Enigma Simulator here:
  2. E.L.

    E.L. Moderator of Lead Moderator Emeritus Founding Member

  3. RightHand

    RightHand Been There, Done That RIP 4/15/21 Moderator Moderator Emeritus Founding Member

    March 4, 1941: 14 German sailors killed as British attack fails to capture Enigma.

    The British navy raids a German position off the coast of Norway and inside the Arctic Circle-the Lofoten Islands. The raid, code name Operation Claymore, destroys the armed German trawler Krebs --but fails to achieve its objective, the capture of an Enigma coding machine.

    The Brits severely damaged the trawler, killed 14 German sailors, took another 25 prisoner, and destroyed the Germans' local stockpile of oil. While the attack boosted British public morale temporarily, the Enigma machine still eluded the British military. The commander of the Krebs, Lieutenant Hans Kupfinger, threw it overboard before he was killed in the raid, but the Brits were able to recover documents that gave clues to the Enigma's workings. British intelligence was able to piece together enough of the German coding system to track German naval activity for about five weeks.

    During the Second World War, German military and diplomatic communications were encoded using an electro-mechanical tool codenamed "Enigma". This device consisted of three wheels (chosen from a standard set) which were individually wired to change one letter code to another. To further encrypt the message, after each character, the wheels would be incremented (like a car's odometer) so that a different letter code would be produced for repeated characters. Enigma could only encrypt the twenty-six letters of the alphabet (which means all messages had to be in characters with no numbers, blanks or punctuation). A message was encoded using an agreed to (between the transmitter and receiver) set of wheels with specific starting positions. To encrypt the message, the text was simply keyed into the Enigma's keyboard and a light representing the encoded character was lit. Decoding messages was simply done by reversing the order of the wheels and running through the process again.

    England's ability to decode messages encrypted on "Enigma" machines was characterized as the greatest secret of the Second World War. It was so secret that this capability was unknown outside government circles until the war had been over for thirty years! The reason why "Ultra" (which was the British code name for the decoding effort) was kept secret for so long seems to be motivated by protecting the governments of the time and avoid the embarrassment of having to explain why they allowed the Germans to bomb cities without taking measures to protect civilians. The bombing of Coventry in 1940 was known to Prime Minister Churchill beforehand, who deliberately did not order the evacuation of civilians or the bolstering of anti-aircraft defenses before the raid in fear of tipping off the Germans that they were able to decode their most secret communications.

    The decoding of the "Enigma" messages by the English was accomplished by knowing parts of messages (such as the transmitting station's call letters) and trying every possible wheel and initial position to find those parts of the message that matched. This was done on a variety of elctro-mechanical computing "engines" which were design to run through different combinations as quickly as possible to find the known clear-text parts of the messages. On average, it took six months of effort (with early computers) to "break" one wheel selection and settings. Over the course of the war, the Germans specified several thousand different wheel selections and settings. In this time period (from 1938 to 1945), the British decoded approximately 50'000 messages, of the average 2000 intercepted each day.
    Codebreakers in Poland had started working on the Enigma before the German invasion as well as during the occupation.

    The Americans used their "Magic" program to decode Japanese diplomatic codes (which were used for military communications). The Americans took a different tack from the British and developed decrypting engines based on standard phone switching equipment (the English engines used custom hardware). The American's "engines" were much cheaper, faster and more reliable than their UK counterparts.
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