Editing Cryptanalysis of the Enigma (section)

==General principles==
{{Main|Cryptanalysis}}
The Enigma machines combined multiple levels of movable rotors and plug cables to produce a particularly complex [[Polyalphabetic cipher|polyalphabetic substitution cipher]]. 

During [[World War I]], inventors in several countries realised that a purely random key sequence, containing no repetitive pattern, would, in principle, make a polyalphabetic substitution cipher unbreakable.<ref>{{Harvnb|Singh|1999|p=116}}</ref> This led to the development of [[rotor machine]]s which alter each character in the [[plaintext]] to produce the [[ciphertext]], by means of a scrambler comprising a set of ''rotors'' that alter the electrical path from character to character, between the input device and the output device. This constant altering of the electrical pathway produces a very long period before the pattern—the [[key (cryptography)|key sequence]] or [[substitution alphabet]]—repeats.

Decrypting enciphered messages involves three stages, defined somewhat differently in that era than in modern cryptography.<ref>{{Harvnb|Churchhouse|2002|p=4}}</ref> First, there is the ''identification'' of the system in use, in this case Enigma; second, ''breaking'' the system by establishing exactly how encryption takes place, and third, ''solving'', which involves finding the way that the machine was set up for an individual message, ''i.e.'' the ''message key''.<ref>{{Harvnb|Churchhouse|2002|pp=4,5}}</ref> Today, it is often assumed that an attacker knows how the encipherment process works (see [[Kerckhoffs's principle]]) and ''breaking'' is often used for ''solving'' a key. Enigma machines, however, had so many potential internal wiring states that reconstructing the machine, independent of particular settings, was a very difficult task.