How public-key crypto was born

Mathematical basis for public-key cryptography was kept secret in its early years to avoid revealing how closely U.K. government was working with U.S. National Security Agency.

Tom Espiner Special to CNET News

Public-key cryptography is widely used to secure online transactions. The math behind the technology was devised by U.K. Government Communications Headquarters scientists in the late 1960s and early 1970s.

The discovery was kept secret to avoid revealing how closely GCHQ was working with the U.S. National Security Agency at the time. The breakthrough by GCHQ scientists James Ellis, Clifford Cocks, and Matthew Williamson only came to light in 1997, when their work was declassified.

In public-key cryptography, data is encrypted using a widely distributed public key, and can be decrypted using a private key. Cocks, the GCHQ mathematician who invented the practical method of public-key cryptography in 1973, and Ralph Benjamin, who was GCHQ's chief scientist from 1971 to 1982, told ZDNet UK about their pioneering work.

"Encryption had existed for decades with progressive enhancements," said Benjamin. "There had been dramatic enhancements within the decades with computer technologies and the need for higher security. All through that period, that encryption and decryption were opposites, was a certainty. Non-secret encryption, which came to be known as public-key cryptography, was quite revolutionary."

Read the full Q&A, "GCHQ pioneers on birth of public-key crypto," at ZDNet UK.