At 10:11 PM -0800 11/4/98, Jim Choate wrote:
Forwarded message:
Date: Wed, 4 Nov 1998 21:45:29 -0800 From: Tim May <tcmay@got.net> Subject: Re: TEMPEST laptops
Radio waves scatter...they don't just travel in pure line of sight. And even if they travelled only in line of sight, the reflections from inside the box and then into the room and then off surfaces....
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.)
If the microwaves (for example) are transmitted parallel to the open side it might very well work just fine. It's going to depend on a variety of factors that will preclude such a blanket statement from being valid.
Nope, they'll still get out. The parallel mirror scenario.
Most of the signals that are emitted by a computer are not in the 100dB dynamic range (@2x=3db that's a signal range of 1:33) , more likely 40-50db if that. For a TTL (5V) signal it barely covers 3dB (LOW is <2.5v and a high is >=4.75). There simply is no way in hell a signal with a 3dB range is going to emit a rf signal that is 100dB. There are other logic families with wider dynamic ranges (eg CMOS w/ 18V Vcc can be nearly 18V or approx. about 12dB).
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. --Tim May Y2K: A good chance to reformat America's hard drive and empty the trash. ---------:---------:---------:---------:---------:---------:---------:---- Timothy C. May | Crypto Anarchy: encryption, digital money, ComSec 3DES: 831-728-0152 | anonymous networks, digital pseudonyms, zero W.A.S.T.E.: Corralitos, CA | knowledge, reputations, information markets, Licensed Ontologist | black markets, collapse of governments.