Clifford Cocks

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Clifford Cocks
CB FRS
Clifford-Cocks-FRS.jpg
Clifford Cocks at the Royal Society admissions day in London, July 2015
Born
Clifford Christopher Cocks

(1950-12-28) 28 December 1950 (age 73) [1]
Prestbury, Cheshire, England, United Kingdom
NationalityBritish
Education Manchester Grammar School
Alma mater University of Cambridge (BA)
Known for
Scientific career
Fields Cryptography
Institutions

Clifford Christopher Cocks CB FRS [2] (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 developed an early public-key cryptography (PKC) system. This pre-dated commercial offerings, but due to the classified nature of Cocks' work, it did not become widely known until 1997 when the work was declassified.

Contents

As his work was not available for public review until 1997, it had no impact on numerous commercial initiatives relating to Internet security that had been commercially developed and that were well established by 1997. His work was technically aligned with the Diffie–Hellman key exchange and elements of the RSA algorithm, these well known systems were independently developed and commercialized. [3] [4]

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 PhD student at the University of Oxford, where he specialised in number theory under Bryan Birch, but left academia without finishing his doctorate. [5]

Career

Non-secret encryption

Cocks left Oxford to join Communications-Electronics Security Group (CESG), an arm of GCHQ, in September 1973. Soon after, Nick Patterson told Cocks about James H. Ellis' non-secret encryption, [5] [6] [7] 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 factorization, [8] and did not even write it down at the time. With this insight, he quickly developed what later became known as the RSA encryption algorithm. [9] [10]

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. [8] With a military focus, financial considerations, and low computing power, the power of public-key cryptography was unrealised in both organisations: [5]

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 [8]

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. [8] The British achievement remained secret until 1997. [11]

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 ten years. [12] 24 years after its discovery, on 18 December 1997, Cocks revealed 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

In 1968, Cocks won a silver medal at the 10th International Mathematical Olympiad. [13]

Cocks held the post of Chief Mathematician at GCHQ. He established the Heilbronn Institute for Mathematical Research at the University of Bristol. [14]

Cocks was made a Companion of the Order of the Bath in 2008 (the citation describes him as "Counsellor, Foreign and Commonwealth Office"). [15] He was awarded an honorary degree from the University of Bristol in 2008, [16] and an honorary Doctor of Science from the University of Birmingham in 2015. [17]

With James Ellis and Malcolm Williamson, Cocks was honoured for his part in the development of public-key cryptography by the Institute of Electrical and Electronics Engineers (IEEE) [18] in 2010 and by induction into the Cryptologic Hall of Honor in 2021.

Cocks was elected a Fellow of the Royal Society (FRS) in 2015. [19] 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. [20]

Related Research Articles

<span class="mw-page-title-main">Cipher</span> Algorithm for encrypting and decrypting information

In cryptography, a cipher is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. To encipher or encode is to convert information into cipher or code. In common parlance, "cipher" is synonymous with "code", as they are both a set of steps that encrypt a message; however, the concepts are distinct in cryptography, especially classical cryptography.

<span class="mw-page-title-main">Cryptanalysis</span> Study of analyzing information systems in order to discover their hidden aspects

Cryptanalysis refers to the process of analyzing information systems in order to understand hidden aspects of the systems. Cryptanalysis is used to breach cryptographic security systems and gain access to the contents of encrypted messages, even if the cryptographic key is unknown.

In cryptography, key size or key length refers to the number of bits in a key used by a cryptographic algorithm.

<span class="mw-page-title-main">Diffie–Hellman key exchange</span> Method of exchanging cryptographic keys

Diffie–Hellman (DH) key exchange is a mathematical method of securely exchanging cryptographic keys over a public channel and was one of the first public-key protocols as conceived by Ralph Merkle and named after Whitfield Diffie and Martin Hellman. DH is one of the earliest practical examples of public key exchange implemented within the field of cryptography. Published in 1976 by Diffie and Hellman, this is the earliest publicly known work that proposed the idea of a private key and a corresponding public key.

<span class="mw-page-title-main">Encryption</span> Process of converting plaintext to ciphertext

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<span class="mw-page-title-main">Public-key cryptography</span> Cryptographic system with public and private keys

Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic algorithms based on mathematical problems termed one-way functions. Security of public-key cryptography depends on keeping the private key secret; the public key can be openly distributed without compromising security.

RSA (Rivest–Shamir–Adleman) is a public-key cryptosystem, one of the oldest widely used for secure data transmission. The initialism "RSA" comes from the surnames of Ron Rivest, Adi Shamir and Leonard Adleman, who publicly described the algorithm in 1977. An equivalent system was developed secretly in 1973 at Government Communications Headquarters (GCHQ), the British signals intelligence agency, by the English mathematician Clifford Cocks. That system was declassified in 1997.

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Identity-based encryption (IBE), is an important primitive of identity-based cryptography. As such it is a type of public-key encryption in which the public key of a user is some unique information about the identity of the user. This means that a sender who has access to the public parameters of the system can encrypt a message using e.g. the text-value of the receiver's name or email address as a key. The receiver obtains its decryption key from a central authority, which needs to be trusted as it generates secret keys for every user.

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In cryptography, a semantically secure cryptosystem is one where only negligible information about the plaintext can be feasibly extracted from the ciphertext. Specifically, any probabilistic, polynomial-time algorithm (PPTA) that is given the ciphertext of a certain message , and the message's length, cannot determine any partial information on the message with probability non-negligibly higher than all other PPTA's that only have access to the message length. This concept is the computational complexity analogue to Shannon's concept of perfect secrecy. Perfect secrecy means that the ciphertext reveals no information at all about the plaintext, whereas semantic security implies that any information revealed cannot be feasibly extracted.

Malcolm John Williamson was a British mathematician and cryptographer. In 1974 he developed what is now known as Diffie–Hellman key exchange. He was then working at GCHQ and was therefore unable to publicise his research as his work was classified. Martin Hellman, who independently developed the key exchange at the same time, received credit for the discovery until Williamson's research was declassified by the British government in 1997.

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The Sakai–Kasahara scheme, also known as the Sakai–Kasahara key encryption algorithm (SAKKE), is an identity-based encryption (IBE) system proposed by Ryuichi Sakai and Masao Kasahara in 2003. Alongside the Boneh–Franklin scheme, this is one of a small number of commercially implemented identity-based encryption schemes. It is an application of pairings over elliptic curves and finite fields. A security proof for the algorithm was produced in 2005 by Chen and Cheng. SAKKE is described in Internet Engineering Task Force (IETF) RFC 6508.

References

  1. ↑ Anon (2016). "Cocks, Clifford Christopher" . Who's Who (online Oxford University Press  ed.). Oxford: A & C Black. doi:10.1093/ww/9780199540884.013.U261614.(Subscription or UK public library membership required.)
  2. ↑ Anon (2015). "Mr Clifford Cocks CB FRS". London: Royal Society. Archived from the original on 17 November 2015.
  3. ↑ "Clifford Cocks, James Ellis, and Malcolm Williamson". National Security Agency/Central Security Service. Retrieved 18 November 2023.
  4. ↑ "The Alternative History of Public-Key Cryptography". cryptome.org. Retrieved 18 November 2023.
  5. 1 2 3 In conversation with Clifford Cocks
  6. ↑ "James Ellis' account of the invention of non-secret encryption". Archived from the original on 10 June 2003. Retrieved 10 June 2003.
  7. ↑ "The Open Secret". Wired . Archived from the original on 26 March 2023.
  8. 1 2 3 4 GCHQ pioneers on birth of public-key crypto
  9. ↑ Cocks, C. C. (20 November 1973). "Note on "Non-Secret Encryption"" (PDF). GCHQ. Archived from the original (PDF) on 2018-09-28.
  10. ↑ U.S. patent 6,731,755
  11. ↑ Wired article on public-key cryptography at GCHQ
  12. ↑ Simon Singh (1999). The Code Book: The Secret History of Codes and Code-breaking. Fourth Estate. ISBN   1-85702-879-1.
  13. ↑ Clifford Cocks's results at International Mathematical Olympiad
  14. ↑ In conversation with Clifford Cocks
  15. ↑ "New Year Honours—United Kingdom" (PDF). The London Gazette . 28 December 2007. Retrieved 7 March 2008.
  16. ↑ "Honorary degrees awarded". University of Bristol . Retrieved 7 March 2008.
  17. ↑ "Honorary Graduates of the University of Birmingham since 2000" (PDF).
  18. ↑ IEEE honours GCHQ public-key crypto inventors
  19. ↑ "Mr Clifford Cocks CB FRS". Royal Society. Archived from the original on 24 September 2015.
  20. ↑ Anon (2015). "Certificate of election: EC/2015/07 Cocks, Clifford Christopher". London: royalsociety.org. Archived from the original on 7 May 2009. Retrieved 11 November 2019.
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