Editing Cryptanalysis of the Enigma (section)

{{EngvarB|date=August 2024}}
{{short description|Decryption of the cipher of the Enigma machine}}
{{Use dmy dates|date=October 2019}}

{{Enigma series}}
[[File:EnigmaMachineLabeled.jpg|thumb|The [[Enigma machine]] was used commercially from the early 1920s and was adopted by the militaries and governments of various countries—most famously, [[Nazi Germany]].]]
'''Cryptanalysis of the Enigma ciphering system''' enabled the western [[Allies of World War II|Allies]] in [[World War II]] to read substantial amounts of [[Morse code|Morse-coded]] radio communications of the [[Axis powers]] that had been enciphered using [[Enigma machine]]s. This yielded [[military intelligence]] which, along with that from other decrypted Axis radio and [[teleprinter]] transmissions, was given the codename ''[[Ultra (cryptography)|Ultra]]''.

The Enigma machines were a family of portable [[cipher]] machines with [[rotor machine|rotor]] [[scrambler]]s.<ref>{{citation |last1=Reuvers |first1=Paul |last2=Simons |first2=Marc |title=Enigma Cipher Machine |year=2010 |url=https://www.cryptomuseum.com/crypto/enigma/index.htm |access-date=22 July 2010}}</ref> Good operating procedures, properly enforced, would have made the plugboard Enigma machine unbreakable to the Allies at that time.<ref>{{Harvnb|Welchman|1997|p=3}}</ref><ref>{{Harvnb|Calvocoressi|2001|p=66}}</ref>{{sfn|Huttenhain|Fricke|1945|pp=4,5}}

The German plugboard-equipped Enigma became the principal [[cryptography|crypto-system]] of the [[Third Reich|German Reich]] and later of other Axis powers. In December 1932 it was broken by mathematician [[Marian Rejewski]] at the [[Polish General Staff]]'s [[Cipher Bureau (Poland)|Cipher Bureau]],<ref>{{cite web |title=Poland's Decisive Role in Cracking Enigma and Transforming the UK's SIGINT Operations |url=https://rusi.org/explore-our-research/publications/commentary/polands-decisive-role-cracking-enigma-and-transforming-uks-sigint-operations}}</ref> using mathematical [[permutation group]] theory combined with French-supplied intelligence material obtained from a German spy. By 1938 Rejewski had invented a device, the [[Bomba (cryptography)|cryptologic bomb]], and [[Henryk Zygalski]] had devised his [[Zygalski sheets|sheets]], to make the cipher-breaking more efficient. Five weeks before the outbreak of World War II, in late July 1939 at a conference just south of [[Warsaw]], the Polish Cipher Bureau shared its Enigma-breaking techniques and technology with the French and British.

During the German [[invasion of Poland]], core Polish Cipher Bureau personnel were evacuated via Romania to France, where they established the ''[[PC Bruno]]'' signals intelligence station with French facilities support. Successful cooperation among the Poles, French, and British continued until June 1940, when [[Second Armistice at Compiègne|France surrendered]] to the Germans.

From this beginning, the British [[GCHQ#World War I|Government Code and Cypher School]] at [[Bletchley Park]] built up an extensive cryptanalytic capability. Initially the decryption was mainly of ''[[Luftwaffe]]'' (German air force) and a few ''[[German Army (Wehrmacht)|Heer]]'' (German army) messages, as the ''[[Kriegsmarine]]'' (German navy) employed much more secure procedures for using Enigma. [[Alan Turing]], a [[University of Cambridge|Cambridge University]] mathematician and logician, provided much of the original thinking that led to upgrading of the Polish [[Bomba (cryptography)|cryptologic bomb]] used in decrypting German Enigma ciphers. However, the ''Kriegsmarine'' introduced an Enigma version with a fourth rotor for its [[U-boat]]s, resulting in a prolonged period when these messages could not be decrypted. With the capture of cipher keys and the use of much faster [[Bombe#US Navy Bombe|US Navy bombes]], regular, rapid reading of U-boat messages resumed. Many commentators say the flow of [[Ultra (cryptography)|Ultra]] [[communications intelligence]] from the decrypting of Enigma, [[Lorenz cipher|Lorenz]], and other ciphers shortened the war substantially and may even have altered its outcome.<ref>{{Cite book|title=Intelligence in War|last=Keegan|first=John|publisher=Alfred A. Knopf|year=2003|location=New York}}</ref>