From: Michael Motyka <mmotyka@lsil.com>
Date: Thu, 24 Dec 1998 08:33:31 +0800
To: cypherpunks@Algebra.COM
Subject: Re: Question about 'TEMPEST': UPS
Message-ID: <3681858B.4028@lsil.com>
MIME-Version: 1.0
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>
Now... Just curious, if I simply make my study into a faraday cage via
use of fine (< 1/2 inch) chicken wire, and insulate my power system from
the computer emenations, would that be enough? Chicken wire is not that
expensive, and I think that I could make it look nice on walls.
>

The cages I've used were framed in wood and had several layers of copper
screening. The mesh was like standard window screen, <.125". There were
two, I think sometimes three, layers. The corners/joints were copper
sheet. The screen was soldered to the corners. The doors were stepped or
beveled and had several sets of fingers - indside edge, outside edge,
perhaps one intermediate. Screen makes ventilation easier. Power should
be brought in through a separate, partitioned, shielded box with
filtering in each partition. Phone lines, same thing. You trust your
apps, os and TCP/IP stack to not rat you out? If not, work off-line
always.

One cage I saw had ferrite tiles on the solid walls to minimize internal
reflections which would cut down on leakage too.

Al foil if it were thick enough would be OK but how do you reliably join
edges? Al has a bad habit of oxidizing rapidly in air. I guess you could
fold edges over several times - seems tacky.

Converting your study is non-trivial. The door would look like crap. You
would need the euivalent of a door over the window. Build one in your
garage. Make it out of sections so you can move it. 6' x 8' seems about
right for a couple computers and some lab equip. Is the cost justified?

I wouldn't trust 1/2" galvanized chicken wire for containing anything
but chickens or other non-gnawing furry woodland creatures.

Mike