On Thu, 04 Jan 2001 18:35:44 -0800 Bill Stewart <[EMAIL PROTECTED]> writes:
> >> Its just yet another 'secure' scheme that uses quantum theory
> >> (here, discrete photons; elsewhere, entangled photons)
> >> to detect or prevent leaking bits.
> >>
> >> More elegant than gas-pressurized, pressure-monitored 'secure' cables, but
> >> the same idea.
> >
> >Except that eavesdropping on the quantum key distribution channel is _always_
> >detected (by `laws of nature'), which is not true for these
> pressure-monitored
> >cables.
>
> The theoretical difference _is_ there, but from a practical perspective,
> both are so inconvenient or expensive that even the very paranoid
> won't use them, and the moderately paranoid can use multiple encryption
> algorithms and overly-long keys. If you suppose that quantum crypto
> hardware becomes medium-cheap, people who are connecting RF-shielded
> cages together over distances of a hundred meters to a hundred kilometers
> (if the quantum crypto can go that far unamplified, otherwise ~2km)
> may find it more practical than pressurized cable.
> If you're going less than a hundred meters, stick to pressurized
> cable and armed guards :-)
Actually, `classical' quantum key distribution by polarised or phase-shifted
photons can be achieved up to distances of 100km. This appears to be the limit
of what these systems can achieve. Using a different technique based on EPR
pairs, this limit can be overcome using repeaters.
I believe there is an application for these techniques. Perheps not to secure
mass market e-commerce transactions. But if the hot line between Moskou and
Washingtom was (supposedly) protected by a one-time pad, why not use quantum
cryptography for such an application in the future?
Jaap-Henk
--
Jaap-Henk Hoepman | Come sail your ships around me
Dept. of Computer Science | And burn your bridges down
University of Twente | Nick Cave - "Ship Song"
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