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Clifford Cocks at the Royal Society admissions day in London, July 2015
Clifford Christopher Cocks
28 December 1950
Prestbury, Cheshire, United Kingdom
|Alma mater||University of Cambridge (BA)|
Clifford Christopher Cocks CB FRS (born 28 December 1950) is a British mathematician and cryptographer. In 1973, while working at the United Kingdom Government Communications Headquarters (GCHQ), he invented a public key cryptography algorithm equivalent to what would become (in 1978) the RSA algorithm.
The idea was classified information and his insight remained hidden for 24 years, despite being independently invented by Rivest, Shamir, and Adleman in 1977. Public-key cryptography using prime factorisation is now part of nearly every Internet transaction.
Cocks was educated at Manchester Grammar School and went on to study the Mathematical Tripos as an undergraduate at King's College, Cambridge. He continued as a postgraduate student at the University of Oxford, where he specialised in number theory.
Cocks left Oxford to join Communications-Electronics Security Group (CESG), an arm of GCHQ, in September 1973. Soon after, Cocks was told about James H. Ellis' non-secret encryption,  an idea which had been published in 1969 but never successfully implemented. Several people had attempted creating the required one-way functions, but Cocks, with his background in number theory, decided to use prime factorisation, and did not even write it down at the time.
GCHQ was not able to find a way to use the algorithm, and treated it as classified information. The scheme was also passed to the NSA. With a military focus, and low computing power, the power of public-key cryptography was unrealised in both organisations:
I judged it most important for military use. In a fluid military situation you may meet unforeseen threats or opportunities. ... if you can share your key rapidly and electronically, you have a major advantage over your opponent. Only at the end of the evolution from Berners-Lee [in 1989] designing an open internet architecture for CERN, its adaptation and adoption for the Arpanet ... did public key cryptography realise its full potential. -Ralph Benjamin
In 1977 the algorithm was independently invented and published by Rivest, Shamir and Adleman, who named it after their initials. There is no evidence of a hint or leak, conscious or unconscious, and Cocks has dismissed the idea. The British achievement remained secret until 1997.
In 1987, the GCHQ had plans to release the work, but Peter Wright's Spycatcher MI5 memoir caused them to delay revealing the research by ten years. 24 years after its discovery, on 18 December 1997, Cocks revealed of the GCHQ history of public-key research in a public talk. James Ellis had died on 25 November 1997, a month before the public announcement was made.
In 2001, Cocks developed one of the first secure identity-based encryption (IBE) schemes, based on assumptions about quadratic residues in composite groups. The Cocks IBE scheme is not widely used in practice due to its high degree of ciphertext expansion. However, it is currently one of the few IBE schemes which do not use bilinear pairings, and rely for security on more well-studied mathematical problems.
Cocks was made a Companion of the Order of the Bath in 2008 (the citation describes him as "Counsellor, Foreign and Commonwealth Office"), and was awarded an honorary degree from the University of Bristol in 2008.
In 2010, he, James Ellis and Malcolm Williamson were honoured by the Institute of Electrical and Electronics Engineers (IEEE) for their part in public-key cryptography.
Clifford Cocks is distinguished for his work in cryptography. He was the first to devise a practicable implementation of public key cryptography, and more recently a practicable scheme for identity based public key encryption. Such achievements have been fundamental in ensuring the security of the world's electronic communications, security that we now take for granted.