How to steal data from air-gapped computers
Researchers have developed many ways to extract data from computer systems by developing hidden channels. A computer with an air filter is considered to be a high-cost target, so considerable research has entailed getting data from them-without a network connection.
Robin Harris is Principal Analyst at TechnoQWAN LLC,. He wrote a post in which he tells about four groups to which the hidden channels are divided:
1. Electromagnetic channels vary from eavesdropping of electromagnetic radiation from the memory bus, to leakage from USB ports and cables.
2. Acoustic channels became popular with the advent of hacked smartphones.
3. Thermal channels will ever find a practical hidden use.
4. Optical transmission was a later focus.
This article describes the classification of LEDs. The document has a good introduction to the methods of data filtering, of which Robin borrowed.