Go further · Chapter 13 · 13c · People story
Who really invented public-key encryption?
The short answer (tap to open)
In 1973 Clifford Cocks, a young mathematician at Britain's GCHQ, invented what we now call RSA encryption, four years before the American trio Rivest, Shamir and Adleman published it. His colleagues James Ellis and Malcolm Williamson had the other key ideas. It all stayed secret until 1997, when GCHQ finally let them tell the story.
How did the internet's padlock stay secret for 24 years?
Card 1 · The puzzle
Around 1970 James Ellis, an engineer at GCHQ, the UK's signals intelligence agency in Cheltenham, wonders whether two people could communicate securely without first sharing a secret. He proves it's possible in principle, but can't find the maths to do it.
Card 2 · September 1973
Clifford Cocks, aged 22 and fresh from Cambridge, joins GCHQ. A colleague mentions Ellis's idea over tea. That evening, at home, Cocks finds a way in about half an hour: multiply two large primes, and use the difficulty of factoring (page 13a). It's essentially RSA.
Card 3 · 1974
His friend Malcolm Williamson finds a way for two people to agree a shared secret over an open line, what the world would later call Diffie-Hellman key exchange.
Card 4 · Silence
It's classified. Computers of the day are too slow to use it widely anyway. GCHQ tells nobody outside.
Card 5 · 1976 and 1977
In the US, Whitfield Diffie and Martin Hellman, then Ron Rivest, Adi Shamir and Leonard Adleman, independently publish the same ideas. RSA becomes the foundation of internet security, and its inventors win the Turing Award.
Card 6 · 1997
GCHQ declassifies the story. Cocks gives a public talk about it. Ellis dies a few weeks before the announcement.
Card 7 · The irony
Cocks's 1973 invention is one of the main targets of Shor's quantum algorithm. GCHQ's National Cyber Security Centre now leads the UK's move to new, quantum-safe encryption (chapter 13).
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Invented in Cheltenham, kept secret for 24 years.
The padlock that protects the internet had a hidden first inventor.
Next in the path · Chapter 14
What can quantum computers do today, and what's still to come?
Next in the path