Eric Hughes posted a nice summary of the TEMPEST situation (interception of RF for eavesdropping on computers). I'll just add a few comments.
About Tempest.
The ability to monitor is real; it's more powerful than you would first imagine.
And the NSA has reportedly restricted several papers on this, though they can't do much about the stuff coming from abroad. Their chief concern doesn't seem to be folks like us, but rather concerns about vans parking outside high tech and defense contractors and slurping up what they can from non-TEMPEST (all caps, for some reason) terminals and computers. And someone asked about building Faraday cages. Don't even try! In 1972-3 I worked inside a Faraday cage in the lab of Dr. Paul Hansma (who's now famous for his atomic force microscope work--small world), and it was real tough to shield against high frequencies (above 500 MHz). Modern computers run at 50MHz and faster and the signal edges are of course much faster. RF emissions are a major hassle, and even 30 dB of shielding will still mean enough emissions for a dedicated listener to pick up.
Hal mentions using flat panel displays to combat emissions. This works, as evidenced by the continued existence of Grid Computer. Remember Grid, who came out with these way-expensive gas plasma laptops around 1985/6? The reason they sold so many of those and are still around was that a large number of them were Tempest certified. (Even larger revenues!) I understand that the Tempest spec Grids had a thin layer of gold foil in front of the screen, even so. Yes, gold thin enough to see through.
BTW, I have one of the original magnesium-cased, bubble-memoried GRiD Compasses. Tres elegant (and even "way cool"....Not! It heats up something fierce, with the magnesium case acting as a heat sink). (I got this at Weird Stuff Warehouse, complete with a magnesium-cased disk drive, cables, etc., for $250. Fully functional, but not a lot of software written for "GRiD-OS." Maybe I'll bring it to the next Cypherpunks meeting.)
monitoring easier. It's safe to presume that there is some amazing stuff going on. Read The Puzzle Palace for more hints. (Like the valley in WV which is one big antenna.)
Ditto on this book recommendation: all would-be cypherpunks should read James Bamford's "The Puzzle Palace." Though published in 1982, it revealed a lot about such "No Such Agency," so much so that the director of NSA, upon encountering Bamford at a dinner, refused to shake his hand and said "Sir, I consider you an unindicted felon!"
Emissions monitoring is also all economics. The price to monitor increases with each more sophisticated attack. CRT's are easy, CPU's are hard. I would like to see public research in this area, just like there is public research in cryptography. Until the public has a better idea of what various attacks cost, there can't be rational decisions about emissions security.
I think the longterm solution to this problem is the same as that for the key problem: small, highly portable, self-contained computers for doing the most sensitive work and for providing passwords to remote systems. Smartcards are one approach, though they obviously are highly constrained in what they can do other than act as ATM or VISA cards. (Laptops are one idea. Following Eric's suggestion that we look into TEMPEST issues, perhaps we could "rate" different laptops and PCs for emissions. Just a thought.) Apple's "Newton" PDA ("Personal Digital Assistant"), General Magic's whatever (talk to Fen L., who works there, but who won't say much), Eo's Hobbit-based PDA, and other systems (Sharp, Casio, etc.), offer a better platform, at least for the long term. With 100 MIPS performance, LCD screens, and no dangling keyboards and cables, these gizmos should be favorably positioned for security-conscious applications. RF emissions should be low to begin with (and can be characterized, of course); additional shielding should be easier to achieve than with full-sized units. PDAs also are small enough that people will carry them everywhere, thus both enhancing security against tampering, and also making them workhorses for security applications. With a good interface to desktop machines, the critical security functions can be done inside the PDA (e.g., accessing a terminal or remote system using zero knowledge protocols, where the PDA answers a challenge question without revealing the actual password or whatever secret key). The announced PDAs also have slots for "PCMCIA" cards, small credit-card-sized cards that can add functionality and memory. The lack of a keyboard in the smallest of these units will be a limit (though external keyboards are options...and with some care, these keyboards can even be made TEMPEST class, though leakage will still persist. A battery-operated keyboard with fiber-optic link to the PDA might be one approach.). The issue of hooking these PDAs to desktop machines and networks is an interestesting one. Wirless links would seem to be risky, except that if all critical computations are done _inside_ the PDA then what gets transmitted is not really "fragile" (in the eavesdropping sense). I suspect that someone will offer a small fiber optic link (like the one I have going between my CD player and my DAT machine). And it will be a couple of years before these become common. But it's about 2-3 years from now that our mission gets really interesting, anyway. Digital money, anonymous voting and conferences (imagine using wireless, encrypted links in meetings to negotiate without opponents knowing..just one of several small business product niches), and all kind of other crypto anarchy ideas. PGP 3.0 for PDAs! -- .......................................................................... Timothy C. May | Crypto Anarchy: encryption, digital money, tcmay@netcom.com | anonymous networks, digital pseudonyms, zero 408-688-5409 | knowledge, reputations, information markets, W.A.S.T.E.: Aptos, CA | black markets, collapse of governments. Higher Power: 2^756839 | PGP 2.0 and MailSafe keys by arrangement.