From: Petro <petro@playboy.com>
Date: Thu, 5 Nov 1998 01:52:57 +0800
To: cypherpunks@Algebra.COM
Subject: Re: TEMPEST laptops
In-Reply-To: <19981101152627.C29091@die.com>
Message-ID: <v04011704b26628ee1ee8@[206.189.103.230]>
MIME-Version: 1.0
Content-Type: text/plain



At 4:02 PM -0500 11/1/98, Tim May wrote:
>
>All good points, but there's a big difference between trying to meet FCC
>emissions requirements for a commercial product that has to meet cost,
>weight, and cosmetic requirements (e.g., a plastic case!), and the scenario
>of making a TEMPEST-like box for a laptop. Ferrite beads and copper tape
>are a lot different from a sealed box made of 10-gauge copper sheet.

	Question:

	What if, instead of trying to entirely prevent leakage, one did a
combination of "redirecting" and "masking" emissions.

	Keep in mind I am asking from a point of total ignorance.

	To break the question down further, a tempest attack is limited by
2 things, distance from the machine (IIRC, the "level" or "strength" of RF
emissions drops by the square of the distance correct?) and (possibly) the
presence of other sources of RF in about the same bands.

	Assuming that the signal level drops by the square of the distance,
then one is far more likely to get tempested from a van outside than an
airplane overhead correct?  In that case, simply design one of Mr. May's
brazed copper boxes so that it is open something similar to:

                 ______________
		|_____         |
                     /         |
                               |
          _                    |
         | |________/          |
         |_____________________|

Where the laptop (or even a full sized tube monitor & computer) is placed
inside.


The other question is how hard, given a _specific_ machine would it be to
create a "RF" jammer? Sort of an active defense versus the passive defense
of a Tempest sheild. build a device that measures the RF coming off a
machine, and rebroadcasts the opposite (i.e. the negation) of the signal?
This should, or could "flatten" the signal making it useless.

Then again, I could be totally wrong.
--
"To sum up: The entire structure of antitrust statutes in this country is a
jumble of economic irrationality and ignorance. It is a product: (a) of a
gross misinterpretation of history, and (b) of rather nave, and certainly
unrealistic, economic theories." Alan Greenspan, "Anti-trust"
http://www.ecosystems.net/mgering/antitrust.html

Petro::E-Commerce Adminstrator::Playboy Ent. Inc.::petro@playboy.com