From: rja14@cl.cam.ac.uk (Ross Anderson)
Subject: Re: Tempest
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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,

Ross

