Re: Question about 'TEMPEST': UPS

[Bill Stewart <bill.stewart@pobox.com>]

At 05:21 PM 12/23/98 -0500, Frederick Burroughs wrote:
>Igor Chudov @ home wrote:
>>  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.
>
>How effective is aluminum foil (crinkled and layered)? It's cheap, easy to install
>and remove, and in concert with some halogen lighting, be host to any number of
>suspicious activities.

Neither one will make a dent from a Tempest perspective,
though the foil might disperse heat enough to protect your dope farm :-)
Bettter to build an RF-tight box for your PC and use fiber cables,
and you'll still need to do really special power filtering.

The Army used to use copper screen cages for computers back in the 70s,
which got about 60dB worth of shielding.  When I ran a TEMPEST-shielded
room in the mid-80s, the specs said (roughly) that you needed 100dB
of shielding for a room with computers in it, and the room technology
we used gave about 110-120dB depending on how tight our door gaskets were.
It used particle board with sheet metal on both sides and special
edge/corner joints, and you packed copper-wool into any loose area
and copper tape on any flat areas that had leaks.  

At the time you needed to be very careful about joints between anything,
because RF just _leaks_, and we watched frequencies up to about 450MHz,
since then-current computer equipment didn't have harmonics at
anything like that high a frequency - but it still didn't take much
of a leak to peg the meters, in spite of that being a .6 meter wavelength.
Well, 1.5MIPS Vaxen are a bit out of date now, 300MHz Pentiums are common,
and they've got all sorts of harmonics out there.
If you want a penetration in the walls, e.g. for air or fiber optic cables,
you needed some ratio I've forgotten between the depth and width of the hole;
A two-inch deep hole could be about 1/4" across -- your 1/2" flat chickenwire
would be pretty transparent.

There's newer stuff now - some kind of carbon-fiber cloth with aluminum in it
that's really nice to wallpaper with, but you still need to handle
all the joints, which is tough to do.


Other than protecting your dope farm, tin foil's not real useful,
though I suppose you could line your hat with it to keep microwaves out :-)
What's scary is that I _have_ seen a catalog (mostly NewAgey health scams)
that sold RF-shielded hats; I forget if they were metal-lined or carbon-fiber.
				Thanks! 
					Bill
Bill Stewart, bill.stewart@pobox.com
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