Tyler's Education

Bill Stewart bill.stewart at pobox.com
Sun Jul 4 23:26:29 PDT 2004

As far as education goes, if you're constantly seeing black vans
with big funky antennas on them parked in front of your house
any time you're on the computer, you've really got far more serious
worries than just a bit of TEMPEST.  It's either time to line up
your lawyers because of stuff you do know you've been doing,
or else time to get your shrink to up your meds a bit.

>On Sat, 3 Jul 2004, Major Variola (ret) wrote:
> > And digital edges are sharp, in the Ghz even when the "clock" is in the 
> Mhz.
> > And boxes need ventilation slots.
>... water cooling ....
>At 07:35 PM 7/3/2004, Thomas Shaddack wrote:
>I expect much bigger problem in the attached cables and connectors.

It's been 15-20 years since I worked on TEMPEST environments,
so technology has overtaken most of what we were doing.
We tested the TEMPEST room at 450 MHz, and needed something like
100-120 dB of shielding to be comfortable with it,
and at those frequencies, you'd easily find leakage if the
copper-wool packing in the joints wasn't tight.
Our VAX ran at something like 10 MHz, and our Sparcstations
might have been as fast as 40 MHz, but basically there wasn't
a lot of high-frequency signal out there, even with harmonics.

The standards for cable penetration were that a waveguide hole
needed to be N wavelengths deep and no more than 1/x wide
(I think it was something like half-wave wide), and most of ours
were an inch or two deep with quarter-inch holes.
That was convenient for running fiber through.
If you stuck a paper-clip about halfway through, the RF meter would peg.
These days, of course, most of the equipment's at much higher frequencies;
I doubt the room would be meaningfully tight with 5GHz machines.

Power connections were filtered, which was much more expensive,
using boxes with big inductors in them.
That part of the job would be much easier today -
the VAX needed three-phase power, and the room drew lots of amps,
as did the two one-ton water-cooled Liebert air conditioners.
That AMD 64-bit CPU might look like a space-heater,
but it really isn't that bad.  And a laptop's a lot better.

We occasionally used TEMPEST-shielded PCs.  They weren't bad -
they had solid metal boxes, and special shielded cables for the
rather heavy keyboards, and the monitors were a bit bulky.
The monitors were mostly CGA or mono text - maybe some EGA,
but basically they were a lot lower end that you'd want today.

Don't expect that laptops will keep you out of trouble -
I once had a laptop projecting its image onto a TV I was near.
The image was out of sync, with three partial images,
and it was probably in the 640x480 days, maybe 800x600, ~1997,
but I'd done nothing special and it was an average TV.
Probably the signal was leaking out the VGA jack on the laptop.

The easy part of TEMPEST monitoring is finding some signal.
The hard part is sorting it out from the noise.
If they're not nearby, they're unlikely to be using TEMPEST on you;
they're much more likely to be tapping your ISP connections.

Bill Stewart  bill.stewart at pobox.com 

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