Message no. 1

From:	Janne Jalkanen <jalkanen@*********.CERN.CH>
Subject:	Re: Quantum Cryptography (one more time)
Date:	Mon, 8 Aug 1994 09:36:38 +0200

On Fri, 5 Aug 1994, Skrub wrote:

> A, would send it. I will assume there is a way yo generate it which will
> control all aspects which are important, and send it to B. You (don't

Yes.

> How does B know if it's correct, won't B looking at it change it?

Yes, but the change will take place at the exact moment of measurement.
He'll get the right data all right, but the quantum will lose it's
original properties, thus one and exactly one measurement can be made on
the photon.

> Therefore it would ALWAYS appear that someone tampered? If B can measure
> the photon than so can the interceptor. The interceptor may then change
> it, but can re emit the whole package and no one will know unless it is
> being timed.

No he cannot, because he does not know what it is like. He can measure
either horizontal or vertical polarization, but since he does not know
WHICH he should measure, he won't get both informations. And to re-emit the
photon he'd need BOTH informations. Otherwise he'll end up with garbage.
And the recipient will know that the data is garbage through some simple
error-correction mechanism.

See my last post on the subject, I don't want to type it all again ;)

> -Skrub

Janne Jalkanen ///! For those who have to fight for it
jalkanen@******.cern.ch /// ! life has a flavor
Janne.Jalkanen@***.fi \\\/// ! the protected will never understand
-'Keep on going...' \XX/ ! (anonymous, Viet Nam, 1968)