At 01:39 AM 5/6/00 -0400, Harvey Newstrom wrote:
>This is the basis of the old DoD Tempest requirements that government
>secured vaults be lead-lined and have no external cables of any kind for
>power or data. A simple truck body does not meet the requirements for
>Tempest shielding.
>
>The ability to read computer screens and keystrokes via radiowaves has been
>around for decades. It is very easy to do, also. Keystrokes produce tiny
>radio bursts when the electrical connection is made. Each key is slightly
>different and has its own fingerprint. Capturing these and displaying
>keystrokes in order is easy. After that, simple code-breaking will
>determine which fingerprint matches which key. For example, in English, the
>letter "e" is most common. The most used key is the space bar, followed by
>the most used letter "e", etc. The longer you monitor, the more exactly the
>frequency table will converge with standard statistical tables.
>
>(Or so I've heard.....)
Seems to me that simply running two or more computers in close proximity
will produce enough hash, especially if all the computers are of the same
make and model, as to obscure the signals from any particular one. It would
not be difficult to arrange some mechanism to "type" on the decoy units -
say, have one PC type out War and Peace on the other, while your typing on
a third machine is obscured.
From my reading on Van Eck, the real information was not from the
keyboard, but from the monitor. The scan rates of the targeted computer are
replicated in the phreaker's monitor, and a sensitive receiver picks up the
RF coming from the screen itself, and uses this as a video signal. You lose
any color information, of course, but high contrast such as black text on
white background can be seen. Since LCD monitors use a different scanning
technique, they would be much less susceptible to this kind of attack.
I recall reading about special fonts specifically designed to provide a
"fuzzy" edge to Van Eck, while remaining easily readable to humans. I wish
I remember where that article was - it's been a few years.
Chuck Kuecker
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