John Zoltak writes:

> Personally, I don't believe that someone could do this. It would require
>  so much storage space and processing power that doesn't exist yet. If we
>  had that much processing power, DES would be useless.

Actually, it was fairly easy to demonstrate that it could be done, that you
could read what someone was typing on a CRT's screen, at least over short
distances.

During the time that Tempest'ing things was the rage, we built standalone word
processors/terminals out of HP2645s. These terminals were extremely radiative
devices, as were almost all devices prior to the initiation of the FCC's rules
on EMI/RFI suppression.

We tried several times to sell the word processors to the military and the
CIA. Most agencies couldn't buy them because of the Tempest rules -- and it
simply wasn't worth our effort to modify and Tempest-qualify the terminals.
However, some agencies did buy them and were restricted to using the machines
only in ray-proof rooms (which are more common than you think).

What actually makes it so easy to accomplish what you might otherwise think
would be difficult was the fact that the CRT drivers and wiring were among the
primary sources of the emitted radiation. In fact, it was easy enough (and
still is if you have a working 2645) that you could demonstrate it to
yourself. The trick was to take a TV set (actually its antenna) and aim it at
the 2645. If you then also put a weak signal on Channel 4, 5, 6, or 7 so as to
create a stable reference pattern and observe whichever channel you selected,
you could actually watch the 2645's various screen patterns change the nature
of the digital interference patterns on the TV. It didn't take much
imagination to believe that you could build a device to properly resync the
CRT's scan information into a perfectly readable replica of the 2645 you were
monitoring.

Wirt Atmar