Clifford Christopher Cocks CB FRS (born 28 December 1950) is a British mathematician and cryptographer. In the early 1970s, while working at the United Kingdom Government Communications Headquarters (GCHQ), he created an early public-key cryptography (PKC) system. This system was developed before commercial versions of PKC became available, but because his work was kept secret, it was not widely known until 1997 when it was declassified.

Since his work was not made public until 1997, it did not influence many commercial projects related to Internet security that had already been developed and were well known by 1997. His system used methods similar to the Diffie–Hellman key exchange and parts of the RSA algorithm. These systems were created independently and later used in commercial products.

Education

Cocks attended Manchester Grammar School and later studied mathematics as an undergraduate at King's College, Cambridge. He then worked on his PhD at the University of Oxford, where he focused on number theory under the guidance of Bryan Birch. However, he left the academic field before completing his doctorate.

Career

In September 1973, Cocks left Oxford to work for the Communications-Electronics Security Group (CESG), which is part of GCHQ. Shortly after, Nick Patterson shared information about James H. Ellis’s idea for non-secret encryption, a concept Ellis had described in 1969 but never successfully used. Many people had tried to create one-way functions, but Cocks, who studied number theory, chose to use prime factorization. He did not write down his idea at the time. This insight helped him quickly develop what later became known as the RSA encryption algorithm.

GCHQ could not find a way to use the algorithm and kept it as secret information. The idea was also shared with the NSA. Because of military goals, limited money, and weak computers, the usefulness of public-key cryptography was not recognized by either organization.

In 1977, the algorithm was independently created and published by Rivest, Shamir, and Adleman, who named it after their initials. There is no evidence of any leaks or hints, and Cocks has denied this idea. The British achievement remained secret until 1997.

In 1987, GCHQ planned to share their work, but Peter Wright’s book about MI5 delayed the release by ten years. Twenty-four years after its discovery, on December 18, 1997, Cocks publicly shared GCHQ’s history of public-key research. James Ellis died on November 25, 1997, a month before the announcement.

In 2001, Cocks created one of the first secure identity-based encryption (IBE) schemes, based on math problems involving quadratic residues in composite groups. The Cocks IBE scheme is not widely used because it produces large amounts of ciphertext. However, it is one of the few IBE schemes that do not use bilinear pairings and rely on well-studied math problems.

In 1968, Cocks won a silver medal at the 10th International Mathematical Olympiad.

Cocks worked as Chief Mathematician at GCHQ. He helped create the Heilbronn Institute for Mathematical Research at the University of Bristol.

In 2008, Cocks was made a Companion of the Order of the Bath (the citation described him as "Counsellor, Foreign and Commonwealth Office"). He received an honorary degree from the University of Bristol in 2008 and an honorary Doctor of Science from the University of Birmingham in 2015.

In 2010, Cocks, along with James Ellis and Malcolm Williamson, was honored by the Institute of Electrical and Electronics Engineers (IEEE) for their role in developing public-key cryptography. He was also inducted into the Cryptologic Hall of Honor in 2021.

In 2015, Cocks was elected a Fellow of the Royal Society (FRS). His certificate of election included details about his work.