The Government Communications Headquarters (GCHQ) is a British intelligence agency responsible for providing signals intelligence (SIGINT) and information assurance. GCHQ provides the UK government and armed forces with signals intelligence as required under the guidance of the Joint Intelligence Committee in support of government policies. The Communications-Electronics Security Group (CESG) is the branch of GCHQ which works to secure the communications and information systems of government and critical parts of UK national infrastructure.
GCHQ was previously known as the Government Code and Cipher School (GC&CS) before 1946.
GCHQ is the responsibility of the UK Secretary of State for Foreign and Commonwealth Affairs, but it is not a part of the Foreign Office, and its Director ranks as a Permanent Secretary.
In the 1920s, GC&CS was successfully reading Soviet Union diplomatic ciphers. However, the British government made details from the decrypts public prompting the Soviet to change their systems to more secure schemes, including the one-time pad, in 1927.
Before World War II, GC&CS was a relatively small department, and staff included Alastair Denniston, Oliver Strachey, Dilly Knox, John Tiltman, Edward Travis, Ernst Fetterlein, Josh Cooper and Hugh Foss.
During the Second World War, GC&CS was based largely at Bletchley Park, reading German Enigma machine ciphers amongst a large number of other systems. In 1940, GC&CS were working on the diplomatic codes and ciphers of 26 countries, tackling over 150 diplomatic cryptosystems.
GC&CS was renamed the "Government Communications Headquarters" in June 1946.
Post-Cold War, the aims of GCHQ were set out by the Intelligence Services Act (1994).
At the end of 2003, GCHQ moved to a new circular HQ (popularly known as 'the Doughnut'), at the time the second-largest public sector building project in Europe with an estimated cost of £337 million. The new building is the base for all of GCHQ's Cheltenham operations.
GCHQ gains its intelligence by monitoring a wide variety of communications and other electronic signals. For this a number of stations have been established in the UK and overseas which are run by the Composite Signals Organisation for GCHQ. The Composite Signals Organisation Station, at Morwenstow near Bude, Cornwall is directly subordinate to GCHQ. The listening stations are at Cheltenham itself, GCHQ CSO Morwenstow, GCHQ CSO Ascension Island, with the U.S.A. at Menwith Hill, and the Columbia Annex (CANX).
In addition to SIGINT, GCHQ provides assistance to Government Departments on their own communications security. This task is given to the Communications-Electronics Security Group (CESG) of GCHQ. CESG is the UK national technical authority for information assurance, including cryptography. CESG does not manufacture security equipment, but works with industry to ensure the availability of suitable products and services, while GCHQ itself can fund research into such areas, for example to the Centre for Quantum Computing at Oxford University.
The public spotlight fell on GCHQ in late 2003 and early 2004 following the sacking of Katharine Gun after she leaked a confidential email from agents at the American National Security Agency to GCHQ agents about the wire-tapping of UN delegates in the run-up to the 2003 Iraq war.
Early in the 1970s the asymmetric key algorithm was invented by a staff member Clifford Cocks, a mathematics graduate. This fact was kept secret until 1997.
GCHQ | Organizations in cryptography | Foreign relations of the United Kingdom | Organisations based in the United Kingdom | United Kingdom intelligence agencies | Cheltenham
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