The other day I found a cheap copy of Arthur C Clarke's ‘2010: Odyssey Two’ in a charity shop. My bookshelf was lacking a copy and I hadn't read it in years, so I snapped it up and re-read it.

At one point it describes the means by which the people on the spaceship secure their communications links back home:

[…] the cipher was based on the product of two hundred-digit prime numbers, and the National Security Agency had staked its reputation on the claim that the fastest computer in existence could not crack it before the Big Crunch at the end of the Universe.

It doesn't take more than a nodding acquaintance with cryptography to recognise the cipher being described here as RSA; but two prime numbers of 100 decimal digits each come to what in modern terminology we would usually describe as a 665-bit RSA key, and that's frankly feeble by modern standards (768-bit keys are a thing of the past and 1024-bit keys are starting to look shaky). For once, Clarke's vaunted foresight seemed to have let him down.

Then I stopped and thought a bit harder. He was writing this around 1980, trying to look thirty years into the future, and not only has he got the encryption algorithm right (well, probably – it isn't 2010 yet and there's still time for surprises, but it doesn't currently look as if RSA will be generally abandoned by then), but he's also within a factor of ten of the right key length – and over a thirty-year period, to be out by even a full factor of ten only needs a 10% error in the doubling period of Moore's Law (although I'd guess it's more likely that what Clarke really failed to anticipate was improved factoring algorithms). So, actually, that's not bad at all!