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4 February 1998
Source: http://www.cesg.gov.uk/storynse.htm
Thanks to Richard Snow

CESG

The History of Non-Secret Encryption

The two main public key cryptography techniques in use today are the Diffie-Hellman key exchange protocol and the RSA encryption system. They were discovered in the academic community in 1976 and 1978 respectively. It was widely rumoured that these techniques were known by UK cryptographers prior to these dates, although this was not officially confirmed until recently. In fact the techniques were first discovered at CESG in the early 1970s. Official confirmation came with the release of the following paper in December 1997 following the death of James Ellis.

The Story Of Non-Secret Encryption (HTML version) by J.H.Ellis (1987) (PostScript version).

The four internal technical papers describing the original systems are now also being made more widely available. These informal technical notes have been set in HTML format for the internet but have not otherwise been edited.

The first demonstration of the ideas behind public-key techniques (which their inventor James Ellis called Non-Secret Encryption) are described in

The Possibility Of Non-Secret Encryption by J.H.Ellis (1970).

A few years later the first practical implementations of these techniques came with the papers

A note on Non-Secret Encryption by C. Cocks (1973), which describes what we now call RSA,

Non-Secret Encryption Using A Finite Field by M. Williamson (1974) , which is essentially Diffie-Hellman, and

Thoughts on cheaper Non Secret Encryption by M. Williamson (1976), which details some improvements.

It is interesting to note that although many different ideas for public-key systems have been proposed, the two which have stood the test of time were the first two to be discovered. It is also interesting that the order of discovery in academia was the opposite to the order of discovery at CESG.