Week 5: Radiation nobody asked for

Van Eck phreaking, TEMPEST, and what it costs to stop a display's own electronics from broadcasting what it shows

22 March 2027

Closing a channel is an engineering cost with a shape, and that shape — not the mechanism — decides who ever pays it.

Open the slides

Every video display, from a cathode-ray tube to a modern digital interface, drives its image with electrical signals that change in step with the picture, and those signals radiate. Wim van Eck’s 1985 paper “Electromagnetic Radiation from Video Display Units: an Eavesdropping Risk?” demonstrated that an ordinary television, retuned, could reconstruct a readable image of a target monitor’s screen from a distance, using equipment inexpensive enough that the paper’s main claim was less “this is possible” than “this is already affordable.”

The channel gave its name to a class of countermeasures — TEMPEST shielding — that predates van Eck’s public paper by decades in classified government use, which is itself informative: the defensive cost of closing an electromagnetic channel was judged worth paying by intelligence agencies long before the attack was public knowledge, and the same shielding remains largely confined to government and military settings today because the cost curve this week’s Bench prices out never became consumer-affordable.

Outline#

• why a raster’s emissions are reconstructible rather than merely detectable: the signal repeats on a known schedule, so a receiver can average it out of the noise floor
• attenuation as a cost curve, not a price: each additional 10 dB costs more than the last, because the remaining leakage moves from the walls to the seams, the ventilation and the mains
• who pays that curve to its end, and what it means that the same disclosure was classified for decades before it was published

Readings

1. Wim van Eck (1985). Electromagnetic Radiation from Video Display Units: An Eavesdropping Risk?. Computers & Security 4(4), 269-286.
2. Jean-Jacques Quisquater and David Samyde (2001). ElectroMagnetic Analysis (EMA): Measures and Counter-Measures for Smart Cards. E-smart 2001, LNCS 2140, 200-210.
3. Markus G. Kuhn (2003). Compromising Emanations: Eavesdropping Risks of Computer Displays. University of Cambridge Technical Report UCAM-CL-TR-577.