The first of several documents related to the US government's TEMPEST programme, obtained by Cryptome.org's John Young under a Freedom of Information Act (FOIA) request, have been posted on his Web site. His original request was denied, but the persistent Young sought an appeal of that decision, which was recently granted in his favour.
No one is quite sure what TEMPEST stands for (some say it's an acronym for: Telecommunications Electronics Material Protected From Emanating Spurious Transmissions". Others say it is a nothing more than a code word), but what it means is quite simple: electromagnetic and acoustic signals which can be remotely detected and interpreted by a spy.
We live in a veritable ocean of electromagnetic radiation, produced by every gizmo we use at home and at work. They all produce signals; and believe it or not, our input to the devices, and their output, create modulations which can be 'read'.
The video signals leaking from your monitor change as you type using a text editor or word processor. It is (just barely) possible to capture the signals and correlate these changes with the actual text, enabling a spy to read over your shoulder, so to speak.
Practically speaking, reading the signals from a person's monitor is no longer feasible, as they are now well shielded due to health paranoia. But then, modems are a notoriously loud class of item, from which the 'noise' can easily be overheard and reconstructed. So are speaker phones, intercoms, outdated CRT monitors, much R&D equipment, you name it. They're all loud enough to be monitored without the physical implantation of any bugging device.
Electrical wiring and telephone lines can transmit such signals by conduction; walls can vibrate subtly, as can pipes, beams, ducts, and the like. The only fix is to silence the equipment, or to actively distort its signal emanations.
The NSA's concern, obviously, is any government equipment which process national security information in plain text. Hence its TEMPEST programme, which explains how to shield equipment and buildings against such exploitation.
And now, thanks to Young, we will all soon be able to figure out how to make our electronic equipment as quiet as the government's. This could be quite useful to academic and corporate researchers, whose activities are of sufficient value to make them targets of TEMPEST-style exploitation.
It will also offer great comfort to the many paranoid boneheads whose egos dispose them to imagine that their deluded rants are of interest to national security operators. Many a blissful hour may now be spent pulling down walls and ceilings and ripping the guts out of suspect computers, televisions, telephones, stereos, microwave ovens, clocks and radios.
Hey, if it keeps them off the streets, we're all for it. ®