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Date: Wed, 4 Nov 1998 23:19:17 -0800 From: Tim May <tcmay@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. ____________________________________________________________________ To know what is right and not to do it is the worst cowardice. Confucius The Armadillo Group ,::////;::-. James Choate Austin, Tx /:'///// ``::>/|/ ravage@ssz.com www.ssz.com .', |||| `/( e\ 512-451-7087 -====~~mm-'`-```-mm --'- --------------------------------------------------------------------