Re: Bare fibers

At 03:20 AM 7/23/96 -0400, Rabid Wombat wrote:
>
>> 
>> Doesn't that make it vulnerable (detectable) to Tempest attacks?

>No.
>Transmitting light via fiber doesn't emit EM.
>Anyway, the original post, as I recall, was about keeping sensitive data 
>on a second hard drive, connected via (very thin, therefore harder to 
>notice) fiber. Tempest monitoring was not a factor.


It occurs to me that a bare fiber could actually be (randomly) hung across 
treetops, roofs, power lines, and various other structures, over a 
many-block distance in suburban areas.    Such a fiber wouldn't be protected 
very well, but it would probably last a few months.  It would also be 
exceedingly hard to find its terminations, and tracing it would be a real 
pain.  (It probably wouldn't be visible against a bright sky more than a 
meter or two away.)

Jim Bell
jimbell@pacifier.com

On Tue, 23 Jul 1996, jim bell wrote:

> At 03:20 AM 7/23/96 -0400, Rabid Wombat wrote:
> >
> >> 
> >> Doesn't that make it vulnerable (detectable) to Tempest attacks?
> 
> >No.
> >Transmitting light via fiber doesn't emit EM.
> >Anyway, the original post, as I recall, was about keeping sensitive data 
> >on a second hard drive, connected via (very thin, therefore harder to 
> >notice) fiber. Tempest monitoring was not a factor.
> 
> 
> It occurs to me that a bare fiber could actually be (randomly) hung across 
> treetops, roofs, power lines, and various other structures, over a 
> many-block distance in suburban areas.    Such a fiber wouldn't be protected 
> very well, but it would probably last a few months.  It would also be 
> exceedingly hard to find its terminations, and tracing it would be a real 
> pain.  (It probably wouldn't be visible against a bright sky more than a 
> meter or two away.)

It also would have little structural integrity - if you attached it to
trees, which sway in the wind, you'd have a broken fiber in a short time.
(The fiber doesn't even need to break, per se; microscopic cracking,
usually at the cladding, will ruin your fiber) (bird strikes would also be
a big problem, mostly for the bird)

Fiber optic cable usually has a kevlar sheath, and exterior aerial grade
fiber generally has a fiberglass rod inserted between the inner sheaths
and the exterior jacket. Water is also a factor - fiber buried in areas
where moisture is likely to be present (almost all applications) is
usually installed with a silicon gel between the interior jackets and the
exterior; water otherwise adheres to the exterior of the cladding, and
expands due to freezing. This causes fine fractures in the cladding, which
makes it more refractive - increasing chromatic dispersion, and therefore
a higher db loss on the cable. 

:)

ob crypto/privacy: Anybody have a good idea for detecting a tap on 
exterior fiber? I'd expect an attacker to have to interupt connectivity, 
terminate both ends of a break, and insert an active device. Thoughts?


> 
> Jim Bell
> jimbell@pacifier.com
>

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In article <Pine.BSF.3.91.960723170725.23791A-100000@mcfeely.bsfs.org>,
Rabid Wombat <wombat@mcfeely.bsfs.org> wrote:

> ob crypto/privacy: Anybody have a good idea for detecting a tap on 
> exterior fiber? I'd expect an attacker to have to interupt connectivity, 
> terminate both ends of a break, and insert an active device. Thoughts?

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.  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.

- -- 
Alan Bostick               | [Spielberg's] latest is TWISTER, a film that
mailto:abostick@netcom.com | gives whole new meaning to the phrase "giant
news:alt.grelb             | sucking sound."  -- Patrick Taggart
http://www.alumni.caltech.edu/~abostick

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Greetings,

	There are other ways of detecting the application of the tap,
but at this time, the chance of detecting the existance of the tap is
reallistically pretty slim. 

	If the fiber is enclosed in a pressurised conduit, then a drop
in the conduit pressure indicates that someone MAY be trying to gain
access to the fiber.  While a pressurized glove-box around the conduit
may allow a break in the conduit to be made without detection, varying
the pressure in the conduit makes that a lot more difficult.  It all
depends on what the value is of the data you are trying to
protect/access.

	-=Chris

On Thu, 25 Jul 1996 11:52:12 -0700, the sage abostick@netcom.com (Alan
Bostick) scribed:

>-----BEGIN PGP SIGNED MESSAGE-----
>
>In article <Pine.BSF.3.91.960723170725.23791A-100000@mcfeely.bsfs.org>,
>Rabid Wombat <wombat@mcfeely.bsfs.org> wrote:
>
>> ob crypto/privacy: Anybody have a good idea for detecting a tap on 
>> exterior fiber? I'd expect an attacker to have to interupt connectivity, 
>> terminate both ends of a break, and insert an active device. Thoughts?
>
>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.  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.
>
>- -- 
>Alan Bostick               | [Spielberg's] latest is TWISTER, a film that
>mailto:abostick@netcom.com | gives whole new meaning to the phrase "giant
>news:alt.grelb             | sucking sound."  -- Patrick Taggart
>http://www.alumni.caltech.edu/~abostick
>
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