Editing Enigma machine (section)

=== Details ===
[[File:Kenngruppenheft.jpg|thumb|German Kenngruppenheft (a U-boat [[codebook]] with grouped key codes)]]
[[File:Enigma keylist 3 rotor.jpg|thumb|Monthly key list number 649 for the German Air Force Enigma, including settings for the reconfigurable reflector (which only change once every eight days)]]
In use, the Enigma required a list of daily key settings and auxiliary documents. In German military practice, communications were divided into separate networks, each using different settings. These communication nets were termed ''keys'' at [[Bletchley Park]], and were assigned [[code name]]s, such as ''Red'', ''Chaffinch'', and ''Shark''. Each unit operating in a network was given the same settings list for its Enigma, valid for a period of time. The procedures for German Naval Enigma were more elaborate and more secure than those in other services and employed auxiliary [[codebook]]s. Navy codebooks were printed in red, water-soluble ink on pink paper so that they could easily be destroyed if they were endangered or if the vessel was sunk.

An Enigma machine's setting (its [[Key (cryptography)|cryptographic key]] in modern terms; ''Schlüssel'' in German) specified each operator-adjustable aspect of the machine:
* Wheel order (''Walzenlage'') – the choice of rotors and the order in which they are fitted.
* Ring settings (''Ringstellung'') – the position of each alphabet ring relative to its rotor wiring.
* Plug connections (''Steckerverbindungen'') – the pairs of letters in the plugboard that are connected together.
* In very late versions, the wiring of the reconfigurable reflector.
* Starting position of the rotors (''Grundstellung'') – chosen by the operator, should be different for each message.

For a message to be correctly encrypted and decrypted, both sender and receiver had to configure their Enigma in the same way; rotor selection and order, ring positions, plugboard connections and starting rotor positions must be identical. Except for the starting positions, these settings were established beforehand, distributed in key lists and changed daily. For example, the settings for the 18th day of the month in the German Luftwaffe Enigma key list number 649 (see image) were as follows:
* Wheel order: IV, II, V
* Ring settings: 15, 23, 26
* Plugboard connections: EJ OY IV AQ KW FX MT PS LU BD
* Reconfigurable reflector wiring: IU AS DV GL FT OX EZ CH MR KN BQ PW
* Indicator groups: lsa zbw vcj rxn

Enigma was designed to be secure even if the rotor wiring was known to an opponent, although in practice considerable effort protected the wiring configuration. If the wiring is secret, the total number of possible configurations has been calculated to be around {{val|3e114}} (approximately 380 bits); with known wiring and other operational constraints, this is reduced to around {{val|e=23}} (76 bits).<ref name="engima_cryptographic_mathematics">{{cite journal |last1=Miller |first1=A. Ray |title=The cryptographic mathematics of Enigma |journal=Cryptologia |date=January 1995 |volume=19 |issue=1 |pages=65–80 |doi=10.1080/0161-119591883773 |url=https://www.tandfonline.com/doi/abs/10.1080/0161-119591883773|url-access=subscription }}</ref> Because of the large number of possibilities, users of Enigma were confident of its security; it was not then feasible for an adversary to even begin to try a [[brute-force attack]].