During World War II, he worked at Britain's secret codebreaking centre, "Station X" at Bletchley Park, where he was one of the most important contributors.- Gordon Welchman
During World War II, the estate housed the Government Code and Cypher School (GC&CS), which regularly penetrated the secret communications of the Axis Powers – most importantly the German Enigma and Lorenz ciphers.- Bletchley Park
The GC&CS team of codebreakers included Alan Turing, Gordon Welchman, Hugh Alexander, Bill Tutte, and Stuart Milner-Barry.- Bletchley Park
During the Second World War it was located at Bletchley Park, where it was responsible for breaking the German Enigma codes.- GCHQ
Even though the goal has been the same, the methods and techniques of cryptanalysis have changed drastically through the history of cryptography, adapting to increasing cryptographic complexity, ranging from the pen-and-paper methods of the past, through machines like the British Bombes and Colossus computers at Bletchley Park in World War II, to the mathematically advanced computerized schemes of the present.- Cryptanalysis
Just before World War II, Welchman was invited by Commander Alastair Denniston to join the Government Code and Cypher School in the event of war.- Gordon Welchman
Sigint missions: comprising maths and cryptanalysis, IT and computer systems, linguistics and translation, and the intelligence analysis unit- GCHQ
However, Welchman's main contributions were to the process of breaking the German Enigma machine cipher.- Gordon Welchman
Around December 1932 Marian Rejewski, a Polish mathematician and cryptologist at the Polish Cipher Bureau, used the theory of permutations, and flaws in the German military-message encipherment procedures, to break message keys of the plugboard Enigma machine.- Enigma machine
Senior staff included Alastair Denniston, Oliver Strachey, Dilly Knox, John Tiltman, Edward Travis, Ernst Fetterlein, Josh Cooper, Donald Michie, Alan Turing, Gordon Welchman, Joan Clarke, Max Newman, William Tutte, I. J. (Jack) Good, Peter Calvocoressi and Hugh Foss.- GCHQ
Gordon Welchman, who became head of Hut 6 at Bletchley Park, has written: "Hut 6 Ultra would never have gotten off the ground if we had not learned from the Poles, in the nick of time, the details both of the German military version of the commercial Enigma machine, and of the operating procedures that were in use."- Enigma machine
The Polish transfer of theory and technology at Pyry formed the crucial basis for the subsequent World War II British Enigma-decryption effort at Bletchley Park, where Welchman worked.- Enigma machine
Key GC&CS cryptanalysts who moved from London to Bletchley Park included John Tiltman, Dillwyn "Dilly" Knox, Josh Cooper, Oliver Strachey and Nigel de Grey.- Bletchley Park
During World War I, inventors in several countries developed rotor cipher machines such as Arthur Scherbius' Enigma, in an attempt to minimise the repetition that had been exploited to break the Vigenère system.- Cryptanalysis
Governments have long recognized the potential benefits of cryptanalysis for intelligence, both military and diplomatic, and established dedicated organizations devoted to breaking the codes and ciphers of other nations, for example, GCHQ and the NSA, organizations which are still very active today.- Cryptanalysis
In 1927 Hugh Foss at the British Government Code and Cypher School was able to show that commercial Enigma machines could be broken, provided suitable cribs were available.- Enigma machine
500 related topics
Alan Mathison Turing (23 June 1912 – 7 June 1954) was an English mathematician, computer scientist, logician, cryptanalyst, philosopher, and theoretical biologist.
During the Second World War, Turing worked for the Government Code and Cypher School (GC&CS) at Bletchley Park, Britain's codebreaking centre that produced Ultra intelligence.
Here, he devised a number of techniques for speeding the breaking of German ciphers, including improvements to the pre-war Polish bombe method, an electromechanical machine that could find settings for the Enigma machine.
The bombe, with an enhancement suggested by mathematician Gordon Welchman, became one of the primary tools, and the major automated one, used to attack Enigma-enciphered messages.
Conel Hugh O'Donel Alexander (19 April 1909 – 15 February 1974), known as Hugh Alexander and C. H. O'D. Alexander, was an Irish-born British cryptanalyst, chess player, and chess writer.
He worked on the German Enigma machine at Bletchley Park during the Second World War, and was later the head of the cryptanalysis division at GCHQ for 25 years.
Other senior colleagues included Stuart Milner-Barry, Gordon Welchman, and Harry Golombek.
Commander Alexander "Alastair" Guthrie Denniston (1 December 1881 – 1 January 1961) was a Scottish codebreaker in Room 40, deputy head of the Government Code and Cypher School (GC&CS) and hockey player.
Following the practice of his superiors at Room 40, he contacted lecturers at Oxford and Cambridge (including Alan Turing and Gordon Welchman) asking if they would be willing to serve if war broke out.
He chose Bletchley as the location for the codebreaking effort because it was at a rail junction on a main line 47 mi north of London with good rail connections to Oxford and Cambridge and MI6 boss, Hugh Sinclair, acquired the Bletchley Park property.
On 26 July 1939, five weeks before the outbreak of war, Denniston was one of three Britons (along with Dilly Knox and Humphrey Sandwith) who participated in the trilateral Polish-French-British conference held in the Kabaty Woods south of Warsaw, at which the Polish Biuro Szyfrów (Cipher Bureau) initiated the French and British into the decryption of German military Enigma ciphers.
Joan Elisabeth Lowther Murray, MBE (née Clarke; 24 June 1917 – 4 September 1996) was an English cryptanalyst and numismatist best known for her work as a code-breaker at Bletchley Park during the Second World War.
Clarke's mathematical abilities were first discovered by Gordon Welchman, in an undergraduate Geometry class at Cambridge.
The Enigma machine was invented by the Germans to encrypt their messages; they strongly believed their code was unbreakable.
In June 1940, Clarke was recruited by her former academic supervisor, Gordon Welchman, to the Government Code and Cypher School (GC&CS).
The bombe was an electro-mechanical device used by British cryptologists to help decipher German Enigma-machine-encrypted secret messages during World War II.
The initial design of the British bombe was produced in 1939 at the UK Government Code and Cypher School (GC&CS) at Bletchley Park by Alan Turing, with an important refinement devised in 1940 by Gordon Welchman.
Ultra was the designation adopted by British military intelligence in June 1941 for wartime signals intelligence obtained by breaking high-level encrypted enemy radio and teleprinter communications at the Government Code and Cypher School (GC&CS) at Bletchley Park.
Much of the German cipher traffic was encrypted on the Enigma machine.
Gordon Welchman wrote,
It has been alleged that "Lucy" was in major part a conduit for the British to feed Ultra intelligence to the Soviets in a way that made it appear to have come from highly placed espionage rather than from cryptanalysis of German radio traffic.
The Cipher Bureau, in Polish: Biuro Szyfrów (, was the interwar Polish General Staff's Second Department's unit charged with SIGINT and both cryptography (the use of ciphers and codes) and cryptanalysis (the study of ciphers and codes, for the purpose of "breaking" them).
In December 1932, the Bureau began breaking Germany's Enigma ciphers.
The British sent Commander Alastair Denniston, head of Britain's Government Code and Cypher School, Dilly Knox, chief British cryptanalyst and Commander Humphrey Sandwith, head of the Royal Navy's intercept and direction-finding stations.
Former Bletchley Park mathematician-cryptologist Gordon Welchman has written: "Ultra would never have gotten 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."
Sir Philip Stuart Milner-Barry (20 September 1906 – 25 March 1995) was a British chess player, chess writer, World War II codebreaker and civil servant.
He worked at Bletchley Park during World War II, and was head of "Hut 6", a section responsible for deciphering messages which had been encrypted using the German Enigma machine.
Upon their return, all three soon joined the Government Code and Cypher School (GC&CS) at Bletchley Park.
Milner-Barry was recruited by mathematician Gordon Welchman, who had been his contemporary at Trinity College; in turn Milner-Barry recruited Hugh Alexander.
Alfred Dillwyn "Dilly" Knox, CMG (23 July 1884 – 27 February 1943) was a British classics scholar and papyrologist at King's College, Cambridge and a codebreaker.
He then joined the Government Code and Cypher School (GC&CS).
At Bletchley Park he worked on the cryptanalysis of Enigma ciphers until his death in 1943.
Hugh Rose Foss (13 May 1902 – 23 December 1971) was a British cryptanalyst.
At Bletchley Park during World War II he made significant contributions both to the breaking of the German Enigma code and headed the section tasked with breaking Japanese Naval codes.
In December 1924 he joined the Government Code and Cipher School.
Gordon Welchman was told that Foss was highly esteemed by the Americans, and says that "before the war he was one of the most brilliant of the professional cryptographers of the Government Code and Cypher School".