Where can I find more info about tempest? Is it a roomwide thing, is it implemented in the cables and housings, or what? I understand that the purpose of Tempest is to prevent people from spying on you via electronic emissions detection. Is this just a glorified Faraday cage?
Both techniques are used. You can either buy TEMPEST-designed equipment, which is designed for low emissions, separation of signals between classified and unclassified components, shielded cables, etc., or you can build a shielded box or room and use special filtered power supplies, fiber optics, etc. The exact standards are classified, but they're a lot stricter than FCC Class A or B. The shielded-room vendors out there also sell to the electromagnetic-compatibility- testing market, who want to have nice quiet rooms to measure emissions from their equipment in. Last time I saw one of these rooms built, about 5 years ago, typical construction used plywood sheets with thick sheet metal on each side, fancy connectors between plywoods, copper-wool crammed in any cracks, and special waveguide meshes for air vents and fiber-optic communication cables, and gives about 100-120 dB shielding for frequencies up to about 1-10GHz. Twenty years ago, typical construction used copper screening and was good to ~60dB. About 3-4 years ago, the typical cost for a TEMPEST PC was ~$4000 more than the non-TEMPEST equivalent, and the equipment was maybe 1 year behind the commercial models due to integration and testing time. TEMPEST mini-computers, if they were small enough, generally took the approach of putting the standard versions of the machine in a box built like the TEMPEST rooms; TEMPEST PCs had a somewhat more integrated design, though they were starting to use commercial motherboards. Bill Stewart