Clifford Cocks

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Clifford Cocks
Born (1950-12-28) 28 December 1950 (age 64)
Prestbury, Cheshire, United Kingdom
Nationality British
Fields Cryptography
Known for RSA encryption

Clifford Christopher Cocks, CB,[1] (born 28 December 1950[2] [3]) is a British mathematician and cryptographer at Government Communications Headquarters (GCHQ). He discovered the widely used encryption algorithm now commonly known as RSA, about three years before it was independently rediscovered by Rivest, Shamir, and Adleman at MIT. He has not been generally recognised for this achievement because his work was classified information, and therefore not released to the public at the time.

Life and work[edit]

In 1968, Cocks won Silver at the International Mathematical Olympiad while at Manchester Grammar School. Cocks went on to study mathematics as an undergraduate at King's College, Cambridge, and was then a postgraduate student at the University of Oxford, where he specialised in number theory, but left to join CESG, an arm of GCHQ, in September 1973.

At GCHQ, Cocks was told about James H. Ellis' "non-secret encryption" and further that since it had been suggested in the late 1960s, no one had been able to find a way to actually implement the concept. Cocks was intrigued, and developed, in 1973, what has become known as the RSA encryption algorithm, realising Ellis' idea. GCHQ appears not to have been able to find a way to use the idea, and in any case, treated it as classified information, so that when it was rediscovered and published by Rivest, Shamir, and Adleman in 1977, Cocks' prior achievement remained unknown until 1997.

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.

As of 2003, Clifford Cocks held the post of Chief Mathematician at GCHQ. He was made a Companion of the Order of the Bath in 2008 (the citation describes him as "Counsellor, Foreign and Commonwealth Office"),[1] and was awarded an honorary degree from Bristol University in 2008.[4]

See also[edit]


  1. ^ a b "New Year Honours—United Kingdom" (PDF). The London Gazette. 2007-12-28. Retrieved 2008-03-07. 
  2. ^ "Clifford Cocks Oration". Bristol University. Archived from the original on 2008-09-15. Retrieved 2008-11-04. 
  3. ^ "Dr Clifford Cocks CB". Bristol University. Retrieved 2011-08-14. 
  4. ^ "Honorary degrees awarded". Bristol University. Retrieved 2008-03-07. 


  • Cocks, Clifford (2001). "An Identity Based Encryption Scheme Based on Quadratic Residues". Cryptography and Coding. Lecture Notes in Computer Science 2260. Springer. pp. 360–363. doi:10.1007/3-540-45325-3_32. 

External links[edit]