Quantum cryptography gets "practical"

[Dave Howe]

Tyler Durden wrote:
> 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.
   Unless I am mistaken as to the Quantum Key Exchange process, only one
photon is ever transmitted, with a known orientation; the system doesn't
use entanglement AFAIK.
   I note also that, as QKE is *extremely* vulnerable to MitM attacks, a
hybrid system (which need only be tactically secure, not strategically
secure) can be used to "lock out" a MitM attacker for long enough that
his presence can be detected, without having to resort to a classical
but unblockable out of band data stream.  I think this is part of the
purpose behind the following paper:
http://eprint.iacr.org/2004/229.pdf
which I am currently trying to understand and failing miserably at *sigh*

> 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".
I have yet to see an advantage to QKE that even mildly justifies the
limitations and cost over anything more than a trivial link (two
buildings within easy walking distance, sending high volumes of
extremely sensitive material between them)


> 
> -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)
> 
> 
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