Enigma machine

In the history of cryptography, the Enigma was a portable cipher machine used to encrypt and decrypt secret messages. More precisely, Enigma was a family of related electro-mechanical rotor machines — there were a variety of different models.

Description

[[Image:Enigma-action.png|right|thumbnail|200px|Enigma encryption for two consecutive letters — current is passed into set of rotors, around the reflector, and back out through the rotors again.

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Note: The greyed-out lines represent other possible circuits within each rotor, which are hard-wired to contacts on each rotor.

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Letter A encrypts differently with consecutive key presses, first to G, and then to C. This is because the right hand rotor has stepped, sending the signal on a completely different route.]]

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Like other rotor machines, the Enigma machine is a combination of mechanical and electrical systems. 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. 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 continual movement of the rotors results in a different cryptographic transformation after each key press.

Related Topics:
Keyboard - Spindle

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The mechanical parts act in such a way as to form a varying electrical circuit — the actual encipherment of a letter is performed electrically. 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. 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. The operator would then proceed to encipher N in the same fashion, and so on.

Related Topics:
Electrical circuit - Lamp

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Current flows from a battery through the bidirectional switch controlled by the depressed key to the plugboard. This plugboard allows the connections between the keyboard and the fixed entry wheel to be easily rewired by an operator. Current proceeds from the plugboard to the fixed entry wheel. This leads into the rotor assembly (or scrambler), where the complex internal wiring of each rotor results in the current passing from one rotor to the next along a convoluted path. After passing through all the rotors, current enters the reflector, which relays the signal back out again through the rotors and the entry wheel — this time via a different path — and proceeds through the plugs and the bi-directional switch from the target letter, to light-up the target lamp.

Related Topics:
Battery - Switch

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Rotors