From: whughes@lonestar.utsa.edu (William W. Hughes)
Subject: Re: Tempest
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In article <1993Apr22.105915.5584@infodev.cam.ac.uk> rja14@cl.cam.ac.uk
(Ross Anderson) writes:
>res@colnet.cmhnet.org (Rob Stampfli) writes:
>> Wouldn't a a second monitor of similar type scrolling gibberish and adjacent
>> to the one being used provide reasonable resistance to tempest attacks?
>We've got a tempest receiver in the lab here, and there's no difficulty in
>picking up individual monitors. Their engineering tolerances are slack enough
>that they tend to radiate on different frequencies. Even where they overlap, you
>can discriminate because they have different line synch frequencies - you can
>lock in on one and average the others out.
>
>The signals are weird in any case, with varying polarisations and all sorts
>of interactions with the building. Just moving a folded dipole around is also
>highly effective as a (randomised) means of switching from one monitor to
>another,
>
Hell, just set up a spark jammer, or some other _very_ electrically-noisy
device. Or build an active Farrady cage around the room, with a "noise"
signal piped into it. While these measures will not totally mask the
emissions of your equipment, they will provide sufficient interference to
make remote monitoring a chancy proposition, at best. There is, of course,
the consideration that these measures may (and almost cretainly will)
cause a certain amount of interference in your own systems. It's a matter
of balancing security versus convenience.

BTW, I'm an ex-Air Force Telecommunications Systems Control Supervisor and
Telecommunications/Cryptographic Equipment Technician.

-- 
                            REMEMBER WACO!
     Who will the government decide to murder next? Maybe you?
[Opinions are mine; I don't care if you blame the University or the State.]
