James Ellis: The British cryptographer who invented public key cryptography before Diffie-Hellman (and kept quiet about it)

When you think of heroic British spies, the image of a mathematician wearing heavy frame glasses, working behind a desk piled with math books, surely is not what comes to mind.

Anonymous Heroes

While the world enjoyed James Bond movies and the West was writing scripts for audiovisual pearls like Rambo, Braddock and Nico (Steven Seagall) a special agent, armed with with pencil and paper, sat creating one of the world’s most powerful military weapons at the time : an asymmetric key cryptosystem.

Asymmetric Cryptography Inventor

Australian-born engineer James H. Ellis sat over a cup of tea and watched as the world of cryptography hailed Whitfield Diffie and Martin Hellman as the inventors of public key cryptography in 1976.

Except this was six years after he had written a paper about public key cryptography. Why didn’t the world know about Ellis’ work before? How come Diffie-Hellman were considered the fathers of asymmetric cryptography for over 20 years?

You may have guessed it from the introduction of this post: Mr. Ellis was a spy working for Britain’s GCHQ (analog to the NSA in the US).

His paper, titled “The Possibility of Secure Non-Secret Digital Encryption”, was secret and meant only for internal circulation at GCHQ. The world never knew about James Ellis’ research work until decades later.

Principia Mathematica

Mr. Ellis reportedly got his idea during World War II, from a Bell Labs researcher who mentioned the possibility of adding some information to communications to make them unintelligible, sending the data over through the airwaves and then removing the extra information again at the receiving end.

This gave him the insight to attempt the same feat using mathematical concepts.

US Patents

Although James Ellis, Whitfield Diffie and Martin Hellman all had the same idea, none of them implemented a viable public key cryptosystem straight away after publishing their results.

This was done by Rivest, Shamir and Adler who later patented the system and developed a commercial product from it named after their initials: RSA.

The RSA patent expired in the year 2000 and since then the system has been incorporated into web browsers, payment systems, privacy guarding systems and all kinds of both proprietary and open source software without the need to pay royalties.

Anonymous Hero

Although the public had no way of knowing about Mr. Ellis’ and his team’s feat before 1997, we now recognize his contribution to the world of cryptography as one of the most important developments of its time.

Sadly, Mr. James Ellis never saw his invention go public as he passed away just days before his colleagues distributed his then classic paper to the public during an event in December 1997.


James H. Ellis Wikipedia Entry

The Alternative History of Public-Key Cryptography

The history of non-secret encryption [PDF]

GCHQ Tribute Page

The Open Secret [1999 Wired Feature]

So who invented public key encryption?

The Story of James Ellis and Clifford Cox [Coursera]

GCHQ has declassified James Ellis’s papers on public key cryptography

Nonsecret Encryption [Springer]

Top photo credit: Ellis Family File Photo