From: Chuck Kuecker (ckuecker@mindspring.com)
Date: Sat Sep 29 2001 - 17:54:31 MDT
At 05:33 PM 9/29/01 -0500, Harvey Newstrom wrote:
>Tempest protection requires lead shielding, special fonts and displays,
>self-contained power supplies, etc. These requirements are standard in
>military secure vaults where computer work is done such that it cannot be
>monitored from outside. I have worked on projects that specifically tested
>and broke such security for military applications. The above information
>have been well-known for decades. More sophisticated techniques are being
>developed all the time.
Just for information - lead is not the best shield for EM emissions, like
Tempest signals. Copper screen, with an opening small enough to act as a
high-pass filter, or copper sheet is much more effective. A Faraday cage is
all you really need, with attention paid to filtering of all power and
signal wiring passing through the enclosure walls. Air vents can be
shielded with copper mesh or sponge. Bonding of all parts to prevent "slot
antennas" from being formed is also important., and door gasketing is
critical. Only a thin sheet of copper is required.
For MAGNETIC fields, you would need an annealed magnetic material in
addition to the electrostatic shield. Fortunately, only low frequency
magnetic signals will penetrate most copper shielding - above a few hundred
Hertz, skin effect will start to have an effect. In any case, the signal
strength drops off much faster than EM radiation.
Lead is only needed to shield against X-rays and higher energy photons,
which carry little information in this case.
I wonder about using two or more "decoy" computers, of the same make and
model as the secured one - driven by some sort of nonsense generator -
perhaps a word processor that is reading in newspaper text via a pneumatic
key actuator - the intent being to drown out the actual information.
LCD displays should be much easier to shield than CRTs, also.
Chuck Kuecker
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