Clifford Cocks

Education

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.

Non-secret encryption

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 didn't even write it down at the time.

With this insight, he quickly developed what later became known as the RSA encryption algorithm.

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.

Public revelation

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 10 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.

Identity-based encryption

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.

Awards and honours

As of 2003, Clifford Cocks held the post of Chief Mathematician at GCHQ. He established the Heilbronn Institute for Mathematical Research at the University of Bristol.

In 1968, Cocks won Silver at the International Mathematical Olympiad. Cocks was elected a Fellow of the Royal Society (FRS) in 2015, his certificate of election reads:

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.

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