James Henry Ellis (
25
September 1924–
25
November 1997) was a British
engineer and
mathematician.
In 1970, while working at the Government
Communications Headquarters (GCHQ) in Cheltenham he conceived of the possibility of "non-secret
encryption", more commonly termed public-key
cryptography.
Early life, education and career
Ellis was born in Australia, although he was conceived in Britain
and grew up in London.
He studied physics at Imperial College
London, and subsequently worked at the Post Office
Research Station at Dollis
Hill. In 1952, Ellis joined GCHQ in Eastcote, West London. In 1965, Ellis moved
to Cheltenham to join the newly-formed Communications-Electronics Security
Group (CESG), an arm of GCHQ.
Discovery of non-secret encryption
Ellis said
that the idea first occurred to him after reading a paper from
World War II by someone at Bell Labs describing a way to protect voice communications by
the receiver adding (and then later subtracting) random
noise. He realised that 'noise' could be applied
mathematically but was not a mathematician and was unable to devise
a way to implement the idea.
Shortly after joining GCHQ in September 1973, after studying
Mathematics at Cambridge University,
Clifford Cocks was told of Ellis' proof and
that no one had been able to figure out a way to implement it. He
went home, thought about it, and returned with the basic idea for
what has become known as the
RSA asymmetric key encryption algorithm. Because
any new and potentially beneficial/harmful technique developed by
GCHQ is by definition
classified
information, the discovery was kept secret.
Not long thereafter, Cocks' friend and fellow mathematician,
Malcolm
Williamson, now also working at GCHQ, after being told of
Cocks' and Ellis' work, thought about the problem of key
distribution and developed what has since become known as
Diffie-Hellman key exchange.
Again, this discovery was classified information and it was
therefore kept secret.
When, a few years later,
Diffie and
Hellman published their 1976 paper,
and shortly after that
Rivest,
Shamir, and
Adleman announced their algorithm, Cocks,
Ellis, and Williamson suggested that GCHQ announce that they had
previously developed both. GCHQ decided against publication at the
time.
At this
point, only GCHQ and the National Security Agency (NSA) in the USA knew about the work of Ellis,
Cocks and Williamson. Whitfield Diffie heard a rumour,
probably from the NSA, and travelled to see James Ellis. The two
men talked about a range of subjects until, at the end, Diffie
asked Ellis "Tell me how you invented public-key cryptography".
After a long pause, Ellis replied "Well, I don't know how much I
should say. Let me just say that you people made much more of it
than we did."
On 18 December 1997, Clifford Cocks delivered a public talk which
contained a brief history of GCHQ's contribution so that Ellis,
Cocks and Williamson received some acknowledgment after nearly
three decades of secrecy. James Ellis died on 25 November 1997, a
month before the public announcement was made.
External links
References