7 Apr 1999 23:41:57 -0000

Or, why I don't read much science fiction.

The March 26 Science has an article on quantum key distribution, henceforth known as QKD. They say that doubts have been raised about the old schemes; Eve might be able to eavesdrop after all. They claim to have proved that if Bob and Alice have quantum computers there is a scheme (given in the article) which allows key exchange over public channels of arbitrary length. Well, they seem to also need a classical authentication method, although I think all quantum schemes have. We don'thave QCs yet, but they say all of these schemes have involved some idealism, and this one might actually come true.

It occurs to me that QC (Q computers) are getting the design-ahead that Drexler predicted for Drextech.

What's scary is the footnote about trojan horses. They ref Lee Smolin as talking about the possibility of "robots" in hidden Hilbert dimensions of the tangled photons which could pop out and reveal information. I'm not sure that phrase means the same thing to them as it does to me. At any rate, they say you can defeat that by teleporting the photons from the last relay station into your trusted area; that either verifies there are no hidden dimensions or simply squishes them, I'm not sure which.

Outline: they say the error correcting codes of QCs can reduce a noisy quantum problem to a noiseless one, and then they describe a procedure, using parity checks of random subset of bits, which can be validly analyzed using classical probability theory, and so you can prove the absence of eavesdropping to some small probability of your choice.

-xx- Damien Raphael Sullivan X-)