Secret coding inventors finally win recognition

By : |October 5, 2010 0

LONDON, UK: "I thought it was quite neat," is how Clifford Cocks describes his invention, kept secret for decades, that eventually helped make secure e-commerce possible. "It was a little ahead of its time."

Cocks, along with James Ellis and Malcolm Williamson, developed public key cryptography in the early 1970s, a revolutionary method of encoding and decoding messages that was far more secure than previous encryption methods.

But because they worked for the British Government Communications Headquarters (GCHQ) intelligence agency, the three mathematicians had to keep quiet about their discovery for two decades while U.S. researchers independently developed similar methods and published their results.



On Tuesday, Ellis, Cocks and Williamson will finally be honoured with an award from the world’s largest technical professional society, the Institute of Electrical and Electronic Engineers (IEEE).

For decades, the credit for the invention had fallen to Massachusetts Institute of Technology cryptographers Ron Rivest, Adi Shamir and Leonard Adleman who published the first public, practical asymmetric cryptography algorithm — RSA, named after their initials.

"I recognised very early on that this was a very major invention," says Peter Hill, a cryptographer and executive committee member of the IEEE, who instigated the process of officially recognising the three Britons.

Hill compares the invention to James Clerk Maxwell’s electromagnetic equations that underpin all modern information and communications technologies, or John Ambrose Fleming’s valve, which laid the foundation for the field of electronics.

Before the invention of public key cryptography, it had always been assumed that the same key used to encrypt a message must be used to decrypt it, meaning that the key was always vulnerable to interception during the transfer between parties.

"The dogma that encryption and decryption are intrinsically equal and opposite had remained absolutely the given wisdom, unchallenged over centuries," says Ralph Benjamin, ex-director of science and technology at GCHQ, who originally assessed the public key technique and coordinated its invention.

With the realisation that the encryption and decryption keys could be different, a new level of secure transmission of messages through asymmetric cryptography — and eventually mass e-commerce — became possible.

Ellis wrote a paper proving the concept in 1969, but it took another four years until the 22-year-old Cocks, then a recent recruit to the GCHQ British signals and information intelligence agency, came up with a way of implementing it.

In public key cryptography, the party that is to receive the secret message creates and publishes a key by multiplying two large prime numbers, and that key is used by the party or parties sending the message to encrypt it.

Only the creator of the key knows the original prime factors — which are near impossible to derive from the published number — and uses them to decrypt the message.

"You needed something that was easy to do and hard to undo. Factoring came to mind straight away," says Cocks.

Asked how long it had taken him to figure out, he says: "It was basically that evening. I’d been talking about it in the afternoon, I went home, and it happened to be an evening when i hadn’t got much to do."

Around the same time, two U.S. researchers, Whitfield Diffie and Martin Hellman, were working on the same idea.

Cocks says he first learned of their work in 1976 when he picked up an edition one lunchtime of Scientific American containing an article called "New Directions in Cryptography."

Today, the RSA algorithm is one of the basic components of the SSL technology used on most ecommerce websites. RSA Security was bought by computer storage giant EMC in 2006 for $2.1 billion.

At the time of their invention, the limits of computational power meant the GCHQ team’s ideas could not be put into practice until the 1980s. Their work was declassified in 1997.

On Tuesday, the IEEE will present its 100th milestone award to Ellis, Cocks and Williamson. Cocks will speak at the ceremony, and James Ellis’s widow will also attend.

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