TEMPEST laptops (fwd)

[Jim Choate]

Forwarded message:

> Date: Wed, 4 Nov 1998 23:19:17 -0800
> From: Tim May <tcmay at got.net>
> Subject: Re: TEMPEST laptops (fwd)

> >It depends on the frequency. Last time I checked a laser or a maser (both
> >are radio waves strictly speaking) travel LOS. The scattering comes from
> >beam divergence and incidental refractions and reflections from the
> >molecules in the air and supported detritus.
> 
> Oh come on, let's not get into sophistry. And lasers are not considered to
> be radio frequency devices by anyone I know of...visible, IR, and UV lasers
> are all treated as _photon_ devices, "light."  (Yes, yes, I know about
> particles vs. waves.)

p-v-w is irrelevent.

No Tim, it's photons as the intermediate vector boson for EM radiation.
*ALL* physicist consider light to be hi-freq radio waves, or radio waves to
be low-freq light. Hell, strictly speaking standing in the middle of a dark
room waving a bar magnet back and forth is a very low freq. flash light.

And you have a physics degree......

> Nope, they'll still get out. The parallel mirror scenario.

Irrelevant.

Last time I checked my microwave was 8 corner reflectors. That says that
ultimately the ray goes back along the way it came with a shift in beam axis.

How a microwave works is that up in one corner is a small grating. Behind
that grating is a magnetron/klystron/etc. tube. That tube sends a beam out
through that little grating. The axis of the tube is slightly mis-aligned
,otherwise the beam would come back into the tube and burn it out - also why
you don't put metal things in there, it disrupts the reflection pattern. As
a consequence of this design the corners and the exact center of the cavity
don't get enough microwave radiation to do much of anything with. If you
were to actualy map the microwaves you'd see beams bouncing back and forth
and not continous coverage. There are actualy spots in every microwave oven
cavity that get zero radiation. Anything put in there cooks as a function of
the water in its neighbor heating up and transfered by the standard
thermodynamic (which is also EM by the way) mechanism.

Test it yourself.

> We're talking about signal strength of the emitted RF  being knocked down
> 80 or 100 dB  by the shielding. This is a common way of talking about the
> effectiveness of a Faraday cage.

True, the point I'm trying to make to you folks is that it *ISN'T* the
absolute level of the signal that you are necessarily concerned with but
rather the dynamic range in that signal. Simply knowing there's a 3mV signal
out there won't do you a damn bit of good unless you have enough signal range
to decode the contents. In actuality you could be emitting GW's of signal and
if there was only say 1uV of signal range you'd never get anything off it.

It just occured to me that one way to weaken TEMPEST is to mask the signals
(not sure exactly how) that are emitted by encrypting (ie whitening) the
signal when it's on exposed/radiating buss or connector.



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