Quantum cryptography gets "practical"

Tyler Durden camera_lumina at hotmail.com
Tue Oct 5 17:32:35 PDT 2004


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 <DaveHowe at gmx.co.uk>
>To: Email List: Cryptography <cryptography at metzdowd.com>,        Email  
>List: Cypherpunks <cypherpunks at al-qaeda.net>
>Subject: Re: QC Hype Watch: Quantum cryptography gets practical
>Date: Tue, 05 Oct 2004 17:48:30 +0100
>
>R. A. Hettinga wrote:
>>Two factors have made this possible: the
>>vast stretches of optical fiber (lit and dark) laid in metropolitan areas,
>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)

_________________________________________________________________
On the road to retirement? Check out MSN Life Events for advice on how to 
get there! http://lifeevents.msn.com/category.aspx?cid=Retirement





More information about the cypherpunks-legacy mailing list