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Comment by ed25519FUUU | Hacker News Reader

What’s TEMPEST? Something that communicates by vibrating a table?

In my dystopian future theory, the government that has no issue jamming 2 and 5 ghz channels to keep people from talking would probably notice two people on on a table continually picking up And dropping their phones. Why wouldn’t they simply whisper to each other in that scenario?

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TEMPEST is a generic term for extracting data that emanates from channels which were are not supposed to carry data. It’s usually an attack, used to spy on people.

The classic example is pointing a high speed camera at an office window across the street and recording the brightness of the walls. Even if the office computer is hidden out of sight the attacker can reconstruct what’s on screen by analysing subtle changes in brightness reflected off the wall.

> The classic example is pointing a high speed camera at an office window across the street and recording the brightness of the walls. Even if the office computer is hidden out of sight the attacker can reconstruct what’s on screen by analysing subtle changes in brightness reflected off the wall.

Is this feasible now?

Yep

https://www.nassiben.com/lamphone

That was specific for CRTs. You can still exploit diffuse reflections, though that's much harder.

The more classic example is display cables like VGA, DVI and HDMI emanate signals that can be used to reconstruct the image displayed. Doesn't work for newer high speed HDMI though.

Old BBC documentary on the topic

https://www.youtube.com/watch?v=mcV6izFG3vQ

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