Idea: Simplified TEMPEST-shielded unit (speculative proposal)
TEMPEST shielding is fairly esoteric (at least for non-EM-specialists) field. But potentially could be made easier by simplifying the problem. If we won't want to shield the user interface (eg. we want just a cryptographic processor), we may put the device into a solid metal case without holes, battery-powered, with the seams in the case covered with eg. adhesive copper tape. The input and output can be mediated by fibers, whose ports can be the only holes, fraction of millimeter in diameter, carefully shielded, in the otherwise seamless well-grounded box. There are potential cooling problems, as there are no ventilation holes in the enclosure; this can be alleviated by using one side of the box as a large passive cooler, eventually with an externally mounted fan with separate power supply. If magnetic shielding is required as well, the box could be made of permalloy or other material with similar magnetic properties. I am not sure how to shield a display. Maybe taking an LCD, bolting it on the shielded box, and cover it with a fine wire mesh and possibly metalized glass? Using LCD with high response time of the individual pixels also dramatically reduces the value of eventual optical emissions. I also have doubts about the keyboard. Several ideas that could help: We may use optical scanning of the key matrix, with the light fed into and read from the matrix by optical fibers, coming out from a well-shielded enclosure, similar to the I/O lines of the first example. We may use a "normal" keyboard, but modified to use reliably random scanning pattern; that won't reduce the EM emissions of the keyboard, but effectively encrypts them, dramatically reducing their intelligence value. It's then necessary to take precautions about the data cable between the keyboard itself and the computer, where the data go through in plaintext; it's possible to encrypt it, or to use a fiber. As really good shielding of complicated cases is difficult to achieve, the primary objective of this approach is to put everything into simple metallic boxes with as few and as small ports as possible, which should be comparatively easy to manufacture, replacing the special contacting of removable panels with disposable adhesive copper tape (the only reason to go inside is replacing batteries, and the tape together with other measures may serve as tamperproofing), and replacement of all potentially radiating external data connections with fiber optic. I should disclaim I have nothing that could vaguely resemble any deeper knowledge of high frequencies; therefore I lay out the idea here and wonder if anyone can see holes in it (and where they are).
On Dec 14, 2003, at 8:33 PM, Thomas Shaddack wrote:
TEMPEST shielding is fairly esoteric (at least for non-EM-specialists) field. But potentially could be made easier by simplifying the problem.
If we won't want to shield the user interface (eg. we want just a cryptographic processor), we may put the device into a solid metal case without holes, battery-powered, with the seams in the case covered with eg. adhesive copper tape. The input and output can be mediated by fibers, whose ports can be the only holes, fraction of millimeter in diameter, carefully shielded, in the otherwise seamless well-grounded box. There are potential cooling problems, as there are no ventilation holes in the enclosure; this can be alleviated by using one side of the box as a large passive cooler, eventually with an externally mounted fan with separate power supply. If magnetic shielding is required as well, the box could be made of permalloy or other material with similar magnetic properties.
I am not sure how to shield a display. Maybe taking an LCD, bolting it on the shielded box, and cover it with a fine wire mesh and possibly metalized glass? Using LCD with high response time of the individual pixels also dramatically reduces the value of eventual optical emissions.
I worked inside a Faraday cage in a physic lab for several months. And, later, I did experiments in and around Faraday cages. Shielding is fairly easy to measure. (Using portable radios and televisions, or even using the Software-Defined Radio as a low-cost spectrum analyzer.) My advice? Skip all of the nonsense about building special laptops or computers and special displays with mesh grids over the displays. Those who are _casually_ interested will not replace their existing Mac Powerbooks or Dell laptops with this metal box monster. Instead, devise a metal mesh bag that one climbs into to use whichever laptop is of interest. To reduce costs, most of the bag can be metallized fabric that is not mesh, with only part of it being mesh, for breathability. (Perhaps the head region, to minimize claustrophobia and to allow audio and visual communication with others nearby.) I would imagine a durable-enough metallized fabric bag could be constructed for under a few hundred dollars, which is surely cheaper for most to use than designing a custom laptop or desktop. Or consider heads-up LCD glasses. These have been available for PCs and gamers for a few years (longer in more experimental forms, of course, dating back to the VR days of the late 80s). Sony has had a couple of models, and so have others. Some have video resolutions (PAL, NTSC), some have VGA resolutions. Perfectly adequate for displaying crypto results and requesting input. These very probably radiate little. But of course a lightweight hood, a la the above mesh bag, would drop the emissions by some other goodly amount of dB. Experiments necessary, of course. Interface to a laptop or PC could be as you described it, with shielded cables. Or just use a small PC (Poqet, etc.) and move the keyboard and CPU under the draped hood. Leakage out the bottom, hence the earlier proposal for a full bag, like a sleeping bag. --Tim May
There's a good possibility that Saddam was traced by Tempest sensing, airborne or mundane. The technology is far more sensitive than a decade ago. And with a lot of snooping technology kept obscure by tales of HUMINT, finks, lost laptops and black bag jobs. For less sensitive compromising emanations, BETA, among others, makes portable Tempest units, desktop and room-sized, the devices export-restricted as if munitions. There's a patent on a booth-like Tempest device into which the user climbs, with protection provided for connections, but whether it was ever built is unknown. A slew of firms make Tempest products which can be examined for what shielding works sufficiently well to be placed on NSA's more or less trustworthy Tempest products list: Beyond commercial-grade, NSA is reportedly able to read faint emanations from all known Tempest protection, thanks in part to reviewing products and international sharing among spooks. Those leaked from fiber are now a piece of cake, and not by tapping the glass a la the RU submarine cable escapade and the derring-do of USS Jimmy Carter custom-rigged to hack transoceanic fiber. Tempest snooping at the atomic level is feasible, thanks to physicists who walk among the electrons with supercomputers. As ever, what you don't know is what kills you, and if you are not currently doing research or working on NDA stuff, you're toast. Protecting against the known is what keeps the orchestrated leak industry thriving. Be sure to submit bright inventions to the authorities to get contracts for funding dark ones that work against the grain, then you'll get really swell contracts or offed. Ex-NSA staff are rolling in clover selling commercialized versions of security technology that NSA freely accesses. Reminds of the Brits selling to gullible govs impregnable Enigma machines after WW2.
participants (3)
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John Young -
Thomas Shaddack -
Tim May