> Date: Fri, 19 Sep 2003 11:57:22 -0400
> From: Ian Grigg <[EMAIL PROTECTED]>

> If I understand this correctly, this is both
> an eavesdropping scenario and an MITM scenario.
> 
> In the above, Eve is acting as Mallory, as she
> is by definition intercepting the bits and re-
> sending them on?

As Dave Howe pointed out, Eve is acting as a repeater and tries not to
alter the bits.  This seems a sensible model of eavesdropping for QKD.
The threat is that Alice and Bob might incorporate bits that were seen
by Eve into their key.  If Bob never receives a bit, it won't be used.

> That is, the "Quantum Property" is that Eve can
> be detected because she destroys photos in the
> act of listening, and Mallory, who can resend
> the photons, has only a 50% chance of reading
> each bit correctly in advance, so he can be
> detected after the fact as well, as 25% of his
> bits are wrong.

The terminology "destroy" is used a bit loosely.  I think the
important thing for QKD is that if a photon is measured with the wrong
basis, the information it is carrying about the key is lost.

Ray

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