A Colossus Mark 2 codebreaking computer being operated by Dorothy Du Boisson (left) and Elsie Booker (right), at Bletchley Park, 1943.

A Colossus Mark 2 codebreaking computer being operated by Dorothy Du Boisson (left) and Elsie Booker (right), at Bletchley Park, 1943.

Detail map of Śródmieście, Warszawa, mazowieckie, Poland,Bletchley, Milton Keynes, England, United Kingdom

A: Śródmieście, Warszawa, mazowieckie, Poland, B: Bletchley, Milton Keynes, England, United Kingdom

Highlights of Alan Turing and Colleagues' Cryptanalysis Work at Bletchley Park

Circa 9/1939 to 1945
In 2019 it was announced that Alan Turing would appear on the new Bank of England 50 GBP note. The design shows him in front of an electronic computer that resembles a Colossus II--a computer of the type that Turing used to decipher Enigma code during World War II. The computer plans in the background of the note include a delay line memory--an early electronic memory for a stored program computer that did not exist during World War II.

In 2019 it was announced that Alan Turing would appear on the new Bank of England 50 GBP note. The design shows him in front of an electronic computer that resembles a Colossus II--a computer of the type that Turing used to decipher Enigma code during World War II. The computer plans in the background of the note include a delay line memory--an early electronic memory for a stored program computer that did not exist during World War II.

On September 1, 1939 Germany invaded Poland, beginning World War II. Two days later, on September 3, Britain and France declared war on Germany. The following day Alan Turing appeared for work at the Code Code and Cypher SchoolOffsite Link at Bletchley, England, with the goal of deciphering military communications encoded by means of Enigma machinesOffsite Link.

As early as December 1932 the Biuro SzyfrówOffsite Link ("Cipher Bureau") in WarsawOffsite Link, the Polish interwarOffsite Linkagency charged with both cryptographyOffsite Link  and cryptanalysisOffsite Link, had broken the German Enigma machineOffsite Link cipherOffsite Link.Over the next nearly seven years before World War IIOffsite Link, the Polish "Cipher Bureau" overcame the growing structural and operating complexities of the plugboardOffsite Link-equipped Enigma, the main German cipher device during the Second World War.

Prior to the beginning of World War II, in October 1938 Polish Cipher BureauOffsite Link mathematician and cryptologistOffsite Link Marian RejewskiOffsite Link designed the bombaOffsite Link, or bomba kryptologiczna  ("bomb" or "cryptologic bomb,") a special-purpose machine for breaking German Enigma machine  ciphers. On July 25, 1939 the Biuro Szyfrów revealed Poland's Enigma-decryption techniques and equipment, which it had achieved using the bomba device, to the French and British. Poland thereby made possible the western Allies' vitally important decryption of Nazi German   secret communications (UltraOffsite Link) during World War II.

"Up to July 25, 1939, the Poles had been breaking Enigma messages for over six and a half years without telling their  FrenchOffsite Link  and BritishOffsite Link alliesOffsite Link. On December 15, 1938, two new rotors, IV and V, were introduced (three of the now five rotors being selected for use in the machine at a time). As Rejewski wrote in a 1979 critique of appendix 1, volume 1 (1979), of the official history of British Intelligence in the Second World War, 'we quickly found the [wirings] within the [new rotors], but [their] introduction [...] raised the number of possible sequences of drums from 6 to 60 [...] and hence also raised tenfold the work of finding the keys. Thus the change was not qualitative but quantitative. We would have had to markedly increase the personnel to operate the bombs, to produce the perforated sheetsOffsite Link (60 series of 26 sheets each were now needed, whereas up to the meeting on July 25, 1939, we had only two such series ready) and to manipulate the sheets.'

"Harry HinsleyOffsite Link suggested in British Intelligence . . . that the Poles decided to share their Enigma-breaking techniques and equipment with the French and British in July 1939 because they had encountered insuperable technical difficulties. Rejewski refuted this: 'No, it was not [cryptologic] difficulties [. . .] that prompted us to work with the British and French, but only the deteriorating political situation. If we had had no difficulties at all we would still, or even the more so, have shared our achievements with our allies as our contribution to the struggle against Germany' ' (Wikipedia article on Bomba (cryptography), accessed 12-21-2008).

In the first few months after arriving at Bletchley Turing made a key deduction that led to his development of BanburismusOffsite Link, a cryptanalytic process used by Turing and his co-workers at Bletchley's Hut 8Offsite Link to help break German KriegsmarineOffsite Link (Naval) messages enciphered by Enigma.

"The process used sequentialOffsite Link conditional probabilityOffsite Link to infer information about the likely settings of the Enigma machine. It gave rise to Turing's invention of the banOffsite Link as a measure of the weight of evidence in favour of a hypothesis. This concept was later applied in TuringeryOffsite Link and all the other methods used for breaking the Lorenz cipherOffsite Link.

"The aim of Banburismus was to reduce the time required of the electromechanical BombeOffsite Link machines by identifying the most likely right-hand and middle wheels of the EnigmaOffsite Link. Hut 8 performed the procedure continuously for two years, stopping only in 1943 when sufficient bombe time became readily available. Banburismus was a development of the "clock methodOffsite Link" invented by the Polish cryptanalyst Jerzy RóżyckOffsite Link

To develop Banburismus Turing

"deduced that the message-settings of KriegsmarineOffsite Link EnigmaOffsite Link signals were enciphered on a common G rundstellung (starting position of the rotors), and were then super-enciphered with a bigramOffsite Link and a trigram lookup table. These trigram tables were in a book called the Kenngruppenbuch (K book). However, without the bigram tables, Hut 8 were unable to start attacking the traffic. A breakthrough was achieved after the Narvik pinch in which the disguised armed trawlerOffsite Link Polares, which was on its way to NarvikOffsite Link in Norway, was seized by HMS GriffinOffsite Link in the North SeaOffsite Link on 26 April 1940. The Germans did not have time to destroy all their cryptographic documents, and the captured material revealed the precise form of the indicating system, supplied the plugboard connections and Grundstellung for April 23 and 24 and the operators' log, which gave a long stretch of paired plaintext and enciphered message for the 25th and 26th.

"The bigram tables themselves were not part of the capture, but Hut 8 were able to use the settings-lists to read retrospectively, all the Kriegsmarine traffic that had been intercepted from 22 to 27 April. This allowed them do a partial reconstruction of the bigram tables and start the first attempt to use Banburismus to attack Kriegsmarine traffic, from 30 April onwards. Eligible days were those where at least 200 messages were received and for which the partial bigram-tables deciphered the indicatorsOffsite Link. The first day to be broken was 8 May 1940, thereafter celebrated as "Foss's Day" in honour of Hugh FossOffsite Link, the cryptanalyst who achieved the feat.

"This task took until November that year, by which time the intelligence was very out of date, but it did show that Banburismus could work. It also allowed much more of the bigram tables to be reconstructed, which in turn allowed April 14 and June 26 to be broken. However, the Kriegsmarine had changed the bigram tables on 1 July. By the end of 1940, much of the theory of the Banburismus scoring system had been worked out.

"The First Lofoten pinch from the trawler Krebs on 3 March 1941 provided the complete keys for February - but no bigram tables or K book. The consequent decrypts allowed the statistical scoring system to be refined so that Banburismus could become the standard procedure against Kriegsmarine Enigma until mid-1943" (This and the earlier quotation are from the Wikipedia article on Banburismus, accessed 01-04-2015.)

About December 1940 Alan TuringOffsite Link and Gordon WelchmanOffsite Link at Bletchley ParkOffsite Link designed an improved Bombe cryptanalysis machineOffsite Link for deciphering Enigma messages.

Between 1940 and 1941 Max NewmanOffsite Link and his team at Bletchley, including Turing, created the top-secret Heath Robinson cryptographic computerOffsite Link named after the cartoonist-designer of fantastic machinesOffsite Link. This special-purpose relay computer successfully decoded messages encrypted by EnigmaOffsite Link, the Nazis' first-generation enciphering machine.

In July 1942 Turing developed  the hand codebreaking method known as TuringeryOffsite Link or Turing's Method (playfully dubbed Turingismus by Peter Ericsson, Peter HiltonOffsite Link and Donald MichieOffsite Link)  for use in cryptanalysis of the Lorenz cipherOffsite Link produced by the SZ40 and SZ42Offsite Link teleprinter rotorOffsite Link stream cipherOffsite Link machines, one of the GermansOffsite LinkGeheimschreiber (secret writer) machines. The British codenamed non-MorseOffsite Link traffic "Fish"Offsite Link, and that from this machine "Tunny".

"Reading a Tunny message required firstly that the logical structure of the system was known, secondly that the periodically changed pattern of active cams on the wheels was derived, and thirdly that the starting positions of the scrambler wheels for this message—the message keyOffsite Link—was established.The logical structure of Tunny had been worked out by William TutteOffsite Link and colleagues over several months ending in January 1942. Deriving the message key was called "setting" at Bletchley Park, but it was the derivation of the cam patterns—which was known as "wheel breaking"—that was the target of Turingery.

"German operator errors in transmitting more than one message with the same key, producing a "depth"Offsite Link, allowed the derivation of that key. Turingery was applied to such a key stream to derive the cam settings" (Wikipedia article on Turingery, accessed 01-04-2015).

In 1943 Alan Turing traveled to New York to consult with Claude Shannon and Harry Nyquist at Bell Labs concerning the encryption of “speech signals” between Roosevelt and ChurchillOffsite Link.

In January 1944 the top-secret ColossusOffsite Link programmable cryptanalysis machine designed by Tommy FlowersOffsite Link and his team at the Post Office Research StationOffsite Link, Dollis Hill, in North West London, was installed at Bletchley Park to crack the higher level encryption of the Nazi Lorenz SZ40Offsite Link machine. Colossus employed vacuum tubes and was between one hundred and one thousand times faster than Heath RobinsonOffsite Link. "It exceeded all expectations and was able to derive many of the Lorenz settings for each message within a few hours, compared to weeks previously" (http://googleblog.blogspot.com/2012/03/remembering-colossus-worlds-first.htmlOffsite Link, accessed 03-0-2012). The Colossus machines have been called the first operational programmable electronic digital computers.

On June 1, 1944 the first improved Colossus Mark 2 with 2400 vacuum tubes was operational at Bletchley Park just in time for the Normandy LandingsOffsite Link. By the end of the war there were ten Colossus computers operating. They enabled the decryption of 63,000,000 characters of high-grade German messages. Even though these machines incorporated features of special purpose electronic digital computers, and had incalculable influence on the outcome of WWII, they had little influence in the conventional sense on the development of computing technology because they remained top secret until about 1970.

"The Colossus computers were used to help decipher teleprinterOffsite Link  messages which had been encrypted using the Lorenz SZ40/42Offsite Link machine — British codebreakers referred to encrypted German teleprinter traffic as "FishOffsite Link" and called the SZ40/42 machine and its traffic as 'TunnyOffsite Link'. Colossus compared two data streams, counting each match based on a programmable Boolean functionOffsite Link. The encrypted message was read at high speed from a paper tape. The other stream was generated internally, and was an electronic simulation of the Lorenz machine at various trial settings. If the match count for a setting was above a certain threshold, it would be sent as output to an electric typewriter" (Wikipedia article on Colossus computer, accessed 11-23-2008).

In March 2012 the Colossus Rebuild Project at the National Museum of ComputingOffsite Link at Bletchley Park had completed an operating reconstruction of a Colossus II, after 10 years and over 6,000 man-days of volunteer effort. The Rebuild stands in its historically correct place, the room in H Block, in Bletchley Park, where Colossus No. 9 stood in WW II.

 

Timeline Themes

Related Entries

Alan Turing:

Claude Shannon:

Harry Nyquist: