Actually, that's an interesting point.
In places like downtown NYC, if the fiber doesn't actually go to the basement of a building, it will certainly go within a few 100 feet, so that last hop is trivial. (But the kind of companies this would be targeted for this would already have fiber to the premises or FTTP anyway....however, that fiber will only on occasion make it all the way to the telecom room...the internal building wiring will often be copper.)
However, it's not like you'd have a continuous piece of fiber all the way from Customer X Location A to Customer X Location B...you'd definitely go through at least one fiber distributing frame (FDF) aka an optical "patch panel". However, the connectors will almost certainly be at least slightly anisotropic, so you'd get a wavefunction collapse, or at least diminish the distance you can go.
So I imagine they actually perform a splice and remove the connectors...this will limit you of course to new, high quality fiber (which is extremely isotropic, and I know this for a fact having previously done a lot of testing for PMD, or Polarization Mode Dispersion.)
An interesting thing to think about is the fact that in dense metro areas, you pretty much have a "star" from the CO out to a premise (which is the cause of deployment of "Collapsed SONET Rings"). This means the other photon of your encrypted pair might easily pass through the same CO somewhere, which would make the system suscpetible to a sort of man in the middle attack. Or at least, your fancy quantum crypto system has defaulted back to standard crypto in terms of its un-hackability.
Moral of this story is, even if this thing is useful, you'll probably have a very hard time finding a place it can be deployed and still retain its "advantages".
-TD
From: Dave Howe <[EMAIL PROTECTED]>
To: Email List: Cryptography <[EMAIL PROTECTED]>, Email List: Cypherpunks <[EMAIL PROTECTED]>
Subject: Re: QC Hype Watch: Quantum cryptography gets practical
Date: Tue, 05 Oct 2004 17:48:30 +0100
R. A. Hettinga wrote:which very conveniently was laid from one of your customers to another of your customers (not between telcos?) - or are they talking only having to lay new links for the "last mile" and splicing in one of the existing dark fibres (presumably ones without any repeaters on it)Two factors have made this possible: the vast stretches of optical fiber (lit and dark) laid in metropolitan areas,
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