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For 2,000 years cryptographers were faced with the same insoluble problem. The sender must encrypt a message according to a certain recipe, known as the key, and the receiver also needs to know the key in order to decrypt. The question is, how does the sender communicate the key to the receiver without risking interception? This is known as the key-distribution problem.
The only solution seemed to be for the sender and receiver to meet in person to exchange the key or, more usually, to hire a courier to deliver it. In the 1960s this method was used by banks, businesses, governments and the military. It was a slow, expensive and risky solution, but cryptographers agreed there was no alternative.
However, in the 1970s one group of mavericks set out to find a way to avoid distributing keys. Working in California, independent of the security establishment, they were about to shatter a paradigm that had existed since the birth of cryptography. Their breakthrough, known as public-key cryptography, was further developed into a cipher known as RSA, which is now used to guarantee security on the internet. RSA provides the locks and keys of the Information Age.
The invention of public-key cryptography has been well documented since 1975, but historians were recently shocked by the revelation of similar research that was conducted secretly behind the closed doors of government laboratories. The programme recounts this hitherto unknown story and reveals the British contribution to the most important cryptographic discovery of the century.
Going public
What is public-key cryptography?
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