It can be turned by hand using a grooved finger-wheel which protrudes from the internal cover when closed, as shown in Figure 2. When placed in the machine, a rotor can be set to one of 26 positions. The complexity comes from the use of several rotors in series - usually three or four - and the regular movement of the rotors this provides a much stronger type of encryption. For example, the pin corresponding to the letter E might be wired to the contact for letter T on the opposite face. Three Enigma rotors and the shaft on which they are placed when in use.īy itself, a rotor performs only a very simple type of encryption - a simple substitution cipher. So the continual changing of electrical paths through the unit because of the rotation of the rotors (which cause the pin contacts to change with each letter typed) implements the polyalphabetic encryption which provided Enigma's high security (for the time). The reflector returns the current, via a different path, back through the rotors (5) and entry wheel (4), and proceeds through plug 'S' connected with a cable (8) to plug 'D', and another bi-directional switch (9) to light-up the lamp. Next, the current proceeds through the - unused, so closed - plug (3) via the entry wheel (4) through the wirings of the three (Wehrmacht Enigma) or four (Kriegsmarine M4) rotors (5) and enters the reflector (6). The plugboard allows rewiring the connections between keyboard (2) and fixed entry wheel (4). The current flows from the battery (1) through the depressed bi-directional letter-switch (2) to the plugboard (3). In reality, there are 26 lamps, keys, plugs and wirings inside the rotors. To simplify the example, only four components of each are shown. To explain the Enigma, we use the wiring diagram on the left. The operator would then proceed to encipher N in the same fashion, and so on. For example, when encrypting a message starting ANX., the operator would first press the A key, and the Z lamp might light Z would be the first letter of the ciphertext. When a key is pressed, the circuit is completed current flows through the various components and ultimately lights one of many lamps, indicating the output letter. The mechanical parts act in such a way as to form a varying electrical circuit - the actual encipherment of a letter is performed electrically. The continual movement of the rotors results in a different cryptographic transformation after each key press. The exact mechanism varies, but the most common form is for the right-hand rotor to step once with every key stroke, and occasionally the motion of neighbouring rotors is triggered. The mechanical mechanism consists of a keyboard a set of rotating disks called rotors arranged adjacently along a spindle and a stepping mechanism to turn one or more of the rotors with each key press. Like other rotor machines, the Enigma machine is a combination of mechanical and electrical systems. For a discussion of how Enigma-derived intelligence was put to use, see ULTRA. For the history and techniques of how Enigma was broken, see Cryptanalysis of the Enigma. This article discusses the Enigma machine itself: its components and its procedures. The exact influence of ULTRA is debated, but a typical assessment is that the end of the European war was hastened by two years because of the decryption of German ciphers.Īlthough the Enigma cipher has cryptographic weaknesses, it was, in practice, only their combination with other significant factors which allowed codebreakers to read messages: mistakes by operators, procedural flaws, and the occasional captured machine or codebook. The intelligence gained through this source - codenamed ULTRA - was a significant aid to the Allied war effort. The machine has gained notoriety because Allied cryptologists were able to decrypt a large number of messages that had been enciphered on the machine. The German military model, the Wehrmacht Enigma, is the version most commonly discussed. The Enigma was used commercially from the early 1920s on, and was also adopted by the military and governmental services of a number of nations - most famously by Nazi Germany before and during World War II. More precisely, Enigma was a family of related electro-mechanical rotor machines - comprising a variety of different models. In the history of cryptography, the Enigma was a portable cipher machine used to encrypt and decrypt secret messages.
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