Questions about Ultra (cryptography)
Short answers, pulled from the story.
What was Ultra in World War II cryptography?
Ultra was the designation adopted by British military intelligence in June 1941 for wartime signals intelligence obtained by breaking high-level encrypted enemy communications at Bletchley Park. The name reflected the idea that the intelligence was so valuable it exceeded the highest British security classification of the time, Most Secret, and was therefore regarded as Ultra Secret. It eventually became the standard term among western Allies for all such intelligence.
Who first broke the Enigma cipher machine?
Marian Rejewski and the Polish Cipher Bureau first broke German military Enigma in December 1932, using a combination of mathematics, intelligence from a spy inside the German communications office, and luck. On the 25th of July 1939, the Polish Cipher Bureau handed reconstructed Enigma machines and decryption techniques to the French and British, directly enabling the Ultra programme.
How did Ultra intelligence affect the outcome of World War II?
According to the official historian of British Intelligence, Sir Harry Hinsley, Ultra shortened the war by two to four years. Dwight D. Eisenhower described Ultra as decisive to Allied victory in a letter to Stewart Menzies in July 1945. Hinsley also noted that without Ultra the Allies would still have won, but the war would have been significantly longer.
What was the Lorenz cipher and how was it broken?
The Lorenz SZ 40/42, codenamed Tunny by the British, was an on-line stream cipher teleprinter system used by the German High Command from June 1941 for strategic communications. It was eventually broken using Colossus machines, the first digital programme-controlled electronic computers. Key figures in the Tunny effort included mathematicians W. T. Bill Tutte and Max Newman and electrical engineer Tommy Flowers.
How did the Allies keep Ultra secret during the war?
The Allies used a cover name, Boniface, attributing Ultra intelligence to a fictional MI6 spy network in Germany. For naval operations, they arranged plausible cover stories before acting on intercepts, such as sending search aircraft to make a convincing sighting of a U-boat before attacking it. By the end of the war, around 40 Special Liaison Units served commands around the world, each following strict procedures including destroying intelligence summaries after commanders had read them.
When was the Ultra secret made public and why was it kept secret so long?
The British ban on disclosing Ultra was lifted in 1974, when F. W. Winterbotham published The Ultra Secret. The secrecy lasted nearly 30 years partly because surplus Enigma machines were sold to developing countries after the war, whose traffic was still being read, and partly because Churchill requested recipients of Ultra intelligence to remain silent on the 25th of May 1945. Alan Turing's last two papers on Enigma decryption were not released to Britain's National Archives until 2012.