Milestones:Invention of Public-key Cryptography, 1969 - 1975
Invention of Public-key Cryptography, 1969-1975
At GCHQ, by 1975 James Ellis had proved that a symmetric secret-key system is unnecessary and Clifford Cocks with Malcolm Williamson showed how such 'public-key cryptography' could be achieved. Until then it was believed that secure communication was impossible without exchange of a secret key, with key distribution a major impediment. With these discoveries the essential principles were known but were kept secret until 1997.
The research was carried out in complete secrecy at GCHQ and could not be revealed until it was decided that no further benefit to national security could be achieved by not revealing it. Like the cryptanalysis done during World War 2 at Bletchley Park (now an IEEE Historical Milestone site, since March 2003), the significance of the work was available for public assessment only long after the research was actually carried out. The work by Diffie & Hellman at Stanford and by Rivest, Shamir & Adleman at MIT was published later.
Public-key Cryptography was an outstanding breakthrough. The work of Ellis, Cocks and Williamson at GCHQ was hidden by official secrecy and not revealed until many years later (December 1997). By then, the public recognition had been allocated to the later ‘re-discoveries’ by Diffie, Hellman and Merkle (public key exchange) at Stanford and Rivest, Shamir and Adleman (RSA algorithm) at MIT. The commercial success of products based on these concepts is now well known, and internet e-commerce could hardly have developed without their availability. This was also a major mathematical breakthrough in cryptography, since it represents a solution to a problem previously considered insoluble (e.g. how to communicate securely without having to exchange keys). It has a sociological significance, in showing the contrast between secret classified research and open academic research (and the general need for the latter to stimulate commercial applications).
Ellis died (aged 73) just before public credit for his work could be given.
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