From: Bill Stewart <stewarts@ix.netcom.com>
Date: Fri, 26 Jul 1996 22:05:54 +0800
To: cypherpunks@toad.com
Subject: Re: Bare fibers
Message-ID: <199607260854.BAA23997@toad.com>
MIME-Version: 1.0
Content-Type: text/plain


At 11:52 AM 7/25/96 -0700, abostick@netcom.com (Alan Bostick) wrote:
>As has been mentioned earlier, all an attacker has to do is encourage
>some of the light to exit the fiber, by bending it, contacting it with
>a detector, etc.
>If the detector is sensitive enough, the loss induced by this is minimal.
>This sort of tapping is exactly the sort of thing quantum cryptography
>is supposed to prevent, or at least identify.  

So far, so good.

>Nothing short of quantum methods is going to spot the tap, 
>unless you happen to come across the tap by inspecting the entire
>length of the fiber.

Pressurized conduit is a favorite paranoid technique - if the 
Bad Guy cuts open the conduit to get at the fiber, your alarm
system notices the pressure drop and goes off.
For slightly less paranoid scenarios, you can use heavy narrow
conduit with epoxied joints, and the extra alarm wire or two
to help detect cutting.  For substantially more paranoid types,
you can always fill your conduit with some sort of flammable
substance that reats with air...

#			Thanks;  Bill
# Bill Stewart, +1-415-442-2215 stewarts@ix.netcom.com
# <A HREF="http://idiom.com/~wcs"> 
#			Dispel Authority!