Editing Ultra (cryptography) (section)

==Sources of intelligence==
Most Ultra intelligence was derived from reading radio messages that had been encrypted with cipher machines, complemented by material from radio communications using [[traffic analysis]] and [[direction finding]]. In the early phases of the war, particularly during the eight-month [[Phoney War]], the Germans could transmit most of their messages using [[Landline|land lines]] and so had no need to use radio. This meant that those at Bletchley Park had some time to build up experience of collecting and starting to decrypt messages on the various [[radio network]]s. German Enigma messages were the main source, with those of the German air force,the [[Luftwaffe]] predominating, as they used radio more and their operators were particularly ill-disciplined.

===German===
[[File:Typical Bletchley intercept sheet.jpg|thumb|upright|A typical Bletchley intercept sheet, before decryption and translation]]
[[File:Bletchley decrypt.jpg|thumb|upright|A typical Bletchley intercept sheet, after decryption]]

====Enigma====
{{Main|Cryptanalysis of the Enigma}}
"[[Enigma machine|Enigma]]" refers to a family of electro-mechanical [[Rotor machine|rotor cipher machines]]. These produced a [[Polyalphabetic cipher|polyalphabetic substitution cipher]] and were widely thought to be unbreakable in the 1920s, when a variant of the commercial Model D was first used by the [[Reichswehr]]. The [[German Army (1935–1945)|German Army]] (''Heer''), [[Kriegsmarine|Navy]], Air Force, [[Nazi Party|Nazi party]], [[Gestapo]] and German diplomats used Enigma machines in several variants. [[Abwehr]]  (German military intelligence) used a four-rotor machine without a plugboard and Naval Enigma used different key management from that of the army or air force, making its traffic far more difficult to cryptanalyse; each variant required different cryptanalytic treatment. The commercial versions were not as secure and [[Dilly Knox]] of GC&CS is said to have broken one before the war.

German military Enigma was first broken in December 1932 by [[Marian Rejewski]] and the [[Biuro Szyfrów|Polish Cipher Bureau]], using a combination of brilliant mathematics, the services of a spy in the German office responsible for administering encrypted communications, and good luck.{{sfn|Singh|1999|p=145}}{{sfn|Copeland|2004|pp=231, 232}} The Poles read Enigma to the outbreak of World War II and beyond, in France.{{sfn|Kozaczuk|1984|pp=81–92}} At the turn of 1939, the Germans made the systems ten times more complex, which required a tenfold increase in Polish decryption equipment, which they could not meet.{{sfn|Rejewski|1984|pp=242–43}} On 25 July 1939, the Polish Cipher Bureau handed [[Polish Enigma doubles|reconstructed Enigma machines]] and their techniques for decrypting ciphers to the French and British.{{sfn|Copeland|2004|pp=234, 235}} [[Gordon Welchman]] wrote,

{{Quote|Ultra would never have got off the ground if we had not learned from the Poles, in the nick of time, the details both of the German military Enigma machine, and of the operating procedures that were in use.|Gordon Welchman{{sfn|Welchman|1984|p=289}}}}

At Bletchley Park, some of the key people responsible for success against Enigma included mathematicians [[Alan Turing]] and [[Conel Hugh O'Donel Alexander|Hugh Alexander]] and, at the [[British Tabulating Machine Company]], chief engineer [[Harold Keen]].<ref name="haigh"/>
After the war, interrogation of German cryptographic personnel led to the conclusion that German cryptanalysts understood that cryptanalytic attacks against Enigma were possible but were thought to require impracticable amounts of effort and investment.{{sfn|Bamford|2001|p=17}} The Poles' early start at breaking Enigma and the continuity of their success gave the Allies an advantage when World War II began.{{sfn|Welchman|1984|p=289}}

====Lorenz cipher====
{{Main|Cryptanalysis of the Lorenz cipher}}
In June 1941, the Germans started to introduce on-line [[stream cipher]] [[teleprinter]] systems for strategic point-to-point radio links, to which the British gave the code-name [[Fish (cryptography)|Fish]].{{sfn|Gannon|2006|p=103}} Several systems were used, principally the [[Lorenz cipher|Lorenz SZ 40/42]] (codenamed "Tunny" by the British) and [[Siemens and Halske T52|Geheimfernschreiber]] ("Sturgeon"). These cipher systems were cryptanalysed, particularly Tunny, which the British thoroughly penetrated. It was eventually attacked using [[Colossus computer|Colossus]] machines, which were the first digital programme-controlled electronic computers. In many respects the Tunny work was more difficult than for the Enigma, since the British codebreakers had no knowledge of the machine producing it and no head-start such as that the Poles had given them against Enigma.<ref name="haigh">{{cite journal | url=http://cacm.acm.org/magazines/2017/1/211102-colossal-genius/fulltext | first=Thomas | last=Haigh | title=Colossal Genius: Tutte, Flowers, and a Bad Imitation of Turing | journal=[[Communications of the ACM]] | volume=60 | issue=1 | date=January 2017 | pages=29–35 | doi=10.1145/3018994| s2cid=41650745 | url-access=subscription }}</ref>

Although the volume of intelligence derived from this system was much smaller than that from Enigma, its importance was often far higher because it produced primarily high-level, strategic intelligence that was sent between Wehrmacht high command ([[Oberkommando der Wehrmacht]], OKW). The eventual bulk decryption of Lorenz-enciphered messages contributed significantly, and perhaps decisively, to the defeat of Nazi Germany.<ref name="Hinsley 1993 8">{{Harvnb|Hinsley|1993a|p=8}}</ref><ref name="Brzezinski 2005 18">{{harv|Brzezinski|2005|p=18}}</ref>  Nevertheless, the Tunny story has become much less well known among the public than the Enigma one.<ref name="haigh"/>  At Bletchley Park, some of the key people responsible for success in the Tunny effort included mathematicians [[W. T. Tutte|W. T. "Bill" Tutte]] and [[Max Newman]] and electrical engineer [[Tommy Flowers]].<ref name="haigh"/>

===Italian===
In June 1940, the Italians were using book codes for most of their military messages, except for the Italian Navy, which in early 1941 had started using a version of the Hagelin [[Rotor machine|rotor-based]] cipher machine [[M-209|C-38]].{{sfn|Hinsley|1993a}} This was broken from June 1941 onwards by the [[Italian subsection of GC&CS]] at [[Bletchley Park]].{{sfn|Wilkinson|1993|pp=61–67}}

===Japanese===
In the [[Pacific War|Pacific theatre]], a Japanese cipher machine, called "[[Purple code|Purple]]" by the Americans, was used for highest-level Japanese diplomatic traffic. It produced a polyalphabetic substitution cipher, but unlike Enigma, was not a rotor machine, being built around electrical [[stepping switch]]es. It was broken by the US Army [[Signal Intelligence Service]] and disseminated as ''[[Magic (cryptography)|Magic]]''. Detailed reports by the Japanese ambassador to Germany were encrypted on the Purple machine. His reports included reviews of German assessments of the military situation, reviews of strategy and intentions, reports on direct inspections by the ambassador (in one case, of Normandy beach defences), and reports of long interviews with Hitler.{{sfn|Hinsley|1993a|p=}} The Japanese are said to have obtained an Enigma machine in 1937, although it is debated whether they were given it by the Germans or bought a commercial version, which, apart from the plugboard and internal wiring, was the German ''Heer/Luftwaffe'' machine. Having developed a similar machine, the Japanese did not use the Enigma machine for their most secret communications.

The chief fleet communications code system used by the Imperial Japanese Navy was called [[JN-25]] by the Americans, and by early 1942 the US Navy had made considerable progress in decrypting Japanese naval messages. The US Army also made progress on the [[Japanese army and diplomatic codes|Japanese Army's codes]] in 1943, including codes used by supply ships, resulting in heavy losses to their shipping.