In 1969, a slightly odd Londoner in his 40s made a radical mathematical breakthrough which is applied now whenever cash cards, mobile phones, e-mail and the Web are used. But James Ellis's discovery was published only in late 1997, a month after his death and 20 years after others in the US had solved the same conundrum by their own methods.
Lore holds that half of Ellis's ideas were ridiculous, the other half potentially brilliant. A civil servant of sorts, his habit was to approach a theoretical problem by challenging its most basic assumptions. There is no suggestion that his simple obligation to keep silent about the invention was ever broken. To stay quiet was Mr Ellis's duty, and he was a very dutiful man.
An unlikely guru, he practised low-key cryptography for Britain's Intelligence services.
This was in the muggy days of the Cold War and that shifty world could not have functioned without sturdy, scientifically wrought codes. Cryptography, in essence, is the art of creating successful secrets - and breaking those kept by others.
In Crypto, a new book by Newsweek journalist Steven Levy, the field is described thus: "Its users collaborate to keep secrets in a world of prying eyes. A sender attempts this by transforming a private message to an altered state, a sort of mystery language: encryption".
This has obvious uses in the world of international intrigue, where nothing is as it seems amid snoops, lies, double-talk and back-hand deals.
Levy continues: "Once the message is transformed into a cacophonous babble, potential eavesdroppers are foiled. Only those in possession of the rules of transformation can restore the disorder back to the harmony of the message as it was first inscribed: decryption.
"Those who don't have that knowledge and try to decrypt messages without the secret `keys' are practising `cryptanalysis'."
Levy underlines how critical the field became outside the closed community. In the wealthy, wired-up world where multitudinous messages are sent daily between individuals, companies and governments, it is crucial.
Without encryption, business on the Internet is impossible. Like a house without locks, no information or electronic transactions would be safe. E-commerce, only now in its infancy, would have been stillborn.
Levy's core interest, however, is in the preservation of privacy in an environment where even one's most personal information now circulates on computer systems.
This has relevance in the Republic, where privacy is guarded by the Data Protection Act. Self-regulation and sectoral law is favoured in the US.
Ellis's tale, confined to the epilogue, is a world away from the loners and oddball math-fiends who dominate the rest of the book. Levy seems more assured describing their spontaneous, hippyesque, privacy campaigns in campus and corporate America of the 1980s and 1990s.
The real lone star, however, is Ellis. An Australia-born orphan, his efforts prefigured the work of geeks in the US, who were far more vocal about their obsession. His employers at General Communication Headquarters (GCHQ) ensured his discovery was kept private.
Ellis did not have an especially senior or highly sensitive position at the GCHQ listening post in Cheltenham, where Her Majesty's agents eavesdropped on the world, and still do. Yet the same rules applied to him as his colleagues at the sneakier end of the business. The technology was advanced; the information classified.
The problem he attempted was this: how can a person send a secure, digitally encrypted message to another without exchanging decryption keys in advance? If solved - no easy task, mind - strangers could exchange data privately without using codes agreed in advance.
For cryptographers, who thrive on paranoia, Ellis's successful solution was revolutionary. The basic assumption previously had been that no system could be private if it used a public key. Ellis's theoretical breakthrough was embellished with mathematical help from a colleague. Figured out while in bed one night, his discovery arose from intellectual curiosity. In the UK, the question of a libertarian desire to protect privacy does not seem to have arisen. Among hobbyist cryptographers addressing the same concepts in the US, it did.
Worried about its own security, GCHQ made no moves to publicise the system after its validity was confirmed by other cryptographers, who were, at first, very concerned about the implications of its public element.
Yet Ellis understood the significance of his achievement. A paper he wrote in 1985 said it would be appropriate to tell the story, "in the interests of historical accuracy after it has been demonstrated clearly that no further benefit can be obtained from continued secrecy". It was not published in his lifetime.
In the US, in 1977, Whit Diffie, independently discovered Ellis's solution. Known now as the father of public key cryptography, Diffie was a nerdy mathematician working outside the government, who had something of a personality disorder, a Buffalo Bill beard and a fetish for Datsun motor cars. His discovery was then developed by software sleuths at universities and endorsed later by big-league firms.
IN the years of Ellis's silence, GCHQ's counterparts at the US National Security Agency engaged in a full-scale campaign to fetter the technology derived from Diffie's discovery. According to Levy, Diffie met Ellis once, in 1982. Besides saying "you did more with it than we did", Ellis didn't let the secret out.
At that stage, the troubles of Diffie and his diffuse cabal were only beginning. Their technology - which is at the heart now of a multi-million dollar industry - was routinely blocked by the National Security Agency, whose watchful policy was to place it in the same category as weapons of mass destruction.
While public key encryption is accepted now as the standard system for ecommerce, the regulatory battles fought by companies pushing the technology continued for almost 20 years and the National Security Agency, worried that the technology would fall into enemy hands, initially licensed only weak versions and banned the export of stronger systems.
Two things stand out in his account. The degree to which the US security sought to block the dispersal of knowledge and its antidote, the resilience and ingenuity of "cypherpunks", who sought to undermine rigid control of cryptography by sending new systems around the world, via the Internet.
Encryption still has its limits. Workers sacked for sending questionable e-mails will know too that encryption can stop at the door of their company's system. Nor are its uses universally good - it hides pederast websites.
Still, privacy is crucial when using the connectivity wrought by the Web. Now commonplace in western countries, the Internet has transformed communications. When reading Levy's book, I sent a query to his website. He responded by e-mail within 20 minutes.
Crypto by Steven Levy is published by Allen Lane/Penguin Press (£18.99 in UK)