10.6 P.S.

Although Diffie and Hellman are acknowledged as the inventors of public-key cryptography, the idea was apparently discovered before their papers appeared. GCHQ is responsible for communications intelligence in the United Kingdom, much as NSA is in the United States. And like NSA, its discoveries are often not shared with the scientific community. James H. Eillis, Clifford C. Cocks, and Malcolm J. Williamson were employed at GCHQ in the 1960s. They published internal Computer Electronics Security Group (CESG) reports in the 1970–1976 period [Ellis, 1970; Cocks, 1973; Williamson, 1974, 1976]. There is also a paper [Ellis, 1987] reviewing GCHQ activity in this area. This paper claims they invented the concept of public-key cryptography, motivated as Diffie and Hellman. One system proposed by Cocks was a variant of the RSA system.

The secret environment of the government intelligence agencies worked against the inventors and it remained a secret until its discovery in 1976. To be fair to Cocks, Ellis and Williamson,

  1. The issue of key distribution would not really be a natural problem for cryptographers in the employ of GCHQ to study, and
  2. The need for digital signatures to support E-commerce is also not a likely subject for study.

The real contribution of Diffie–Hellman is not only the invention of asymmetric two-key cryptography, but the realization that there was a real need for it.

The url www.cesg.gov.uk contains links to papers describing the invention by Cocks et al. ...

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