Re: TEMPEST laptops (fwd)

[Tim May <tcmay@got.net>]

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.
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Timothy C. May              | Crypto Anarchy: encryption, digital money,
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