Re: TEMPEST laptops (fwd)
Forwarded message:
Date: Wed, 4 Nov 1998 21:45:29 -0800 From: Tim May <tcmay@got.net> Subject: Re: TEMPEST laptops
Radio waves scatter...they don't just travel in pure line of sight. And even if they travelled only in line of sight, the reflections from inside the box and then into the room and then off surfaces....
It depends on the frequency. Last time I checked a laser or a maser (both are radio waves strictly speaking) travel LOS. The scattering comes from beam divergence and incidental refractions and reflections from the molecules in the air and supported detritus.
Microwave ovens work by having the waves bounce around inside a box. Any significant hole or crack (up to roughly half the wavelength) would let the waves out.
Depends on the size of the hole and location. In most microwave ovens there are definite dead-spots (corners and the exact center of the area are notorius).
An open top box will not work.
If the microwaves (for example) are transmitted parallel to the open side it might very well work just fine. It's going to depend on a variety of factors that will preclude such a blanket statement from being valid.
Unlikely to prevent someone from figuring out what the real signal is. It's very difficult, generally, to hide a signal with another signal. Noise won't work, because noise can be filtered or autocorrelated out. A "spoof" signal can be corrected for.
For these to work there must be a time-correlated aspect to the signal that doesn't appear in the noise. If you mask the signal with the same sort of time correlated cover (eg phase shifting) it also might work.
And we are talking about 100 dB sorts of suppression. Mere factors of a few with fake signals and noise are meaningless on this scale.
The absolute magnitude isn't really important. Most of the signals that are emitted by a computer are not in the 100dB dynamic range (@2x=3db that's a signal range of 1:33) , more likely 40-50db if that. For a TTL (5V) signal it barely covers 3dB (LOW is <2.5v and a high is >=4.75). There simply is no way in hell a signal with a 3dB range is going to emit a rf signal that is 100dB. There are other logic families with wider dynamic ranges (eg CMOS w/ 18V Vcc can be nearly 18V or approx. about 12dB). ____________________________________________________________________ To know what is right and not to do it is the worst cowardice. Confucius The Armadillo Group ,::////;::-. James Choate Austin, Tx /:'///// ``::>/|/ ravage@ssz.com www.ssz.com .', |||| `/( e\ 512-451-7087 -====~~mm-'`-```-mm --'- --------------------------------------------------------------------
At 10:11 PM -0800 11/4/98, Jim Choate wrote:
Forwarded message:
Date: Wed, 4 Nov 1998 21:45:29 -0800 From: Tim May <tcmay@got.net> Subject: Re: TEMPEST laptops
Radio waves scatter...they don't just travel in pure line of sight. And even if they travelled only in line of sight, the reflections from inside the box and then into the room and then off surfaces....
It depends on the frequency. Last time I checked a laser or a maser (both are radio waves strictly speaking) travel LOS. The scattering comes from beam divergence and incidental refractions and reflections from the molecules in the air and supported detritus.
Oh come on, let's not get into sophistry. And lasers are not considered to be radio frequency devices by anyone I know of...visible, IR, and UV lasers are all treated as _photon_ devices, "light." (Yes, yes, I know about particles vs. waves.)
If the microwaves (for example) are transmitted parallel to the open side it might very well work just fine. It's going to depend on a variety of factors that will preclude such a blanket statement from being valid.
Nope, they'll still get out. The parallel mirror scenario.
Most of the signals that are emitted by a computer are not in the 100dB dynamic range (@2x=3db that's a signal range of 1:33) , more likely 40-50db if that. For a TTL (5V) signal it barely covers 3dB (LOW is <2.5v and a high is >=4.75). There simply is no way in hell a signal with a 3dB range is going to emit a rf signal that is 100dB. There are other logic families with wider dynamic ranges (eg CMOS w/ 18V Vcc can be nearly 18V or approx. about 12dB).
We're talking about signal strength of the emitted RF being knocked down 80 or 100 dB by the shielding. This is a common way of talking about the effectiveness of a Faraday cage. --Tim May Y2K: A good chance to reformat America's hard drive and empty the trash. ---------:---------:---------:---------:---------:---------:---------:---- Timothy C. May | Crypto Anarchy: encryption, digital money, ComSec 3DES: 831-728-0152 | anonymous networks, digital pseudonyms, zero W.A.S.T.E.: Corralitos, CA | knowledge, reputations, information markets, Licensed Ontologist | black markets, collapse of governments.
At 1:11 AM -0500 11/5/98, Jim Choate wrote:
Forwarded message:
Date: Wed, 4 Nov 1998 21:45:29 -0800 From: Tim May <tcmay@got.net> Subject: Re: TEMPEST laptops
Radio waves scatter...they don't just travel in pure line of sight. And even if they travelled only in line of sight, the reflections from inside the box and then into the room and then off surfaces....
It depends on the frequency. Last time I checked a laser or a maser (both are radio waves strictly speaking) travel LOS. The scattering comes from beam divergence and incidental refractions and reflections from the molecules in the air and supported detritus.
And both Lasers and Masers scatter under certain conditions. If you can see the laser, it is scattering a bit of [energy light photons] That is what Mr. May is talking about. I was under the (apparently false) impression that things like animal bodies, and ordinary building materials (like wood, Lathe & plaster/drywall) wouldn't stop or significantly bounce the beams back the way you didn't want them to go. I was thinking more of controling the direction of the RF, rather than trying to completely supress it. It doesn't appear that will work.
Microwave ovens work by having the waves bounce around inside a box. Any significant hole or crack (up to roughly half the wavelength) would let the waves out.
Depends on the size of the hole and location. In most microwave ovens there are definite dead-spots (corners and the exact center of the area are notorius).
We're not cooking Hotdogs here, and we aren't using (for the most part) microwaves. Yes, you can heat a hotdog on a PII, but that is more from heat radiation than RF. Microwave ovens also leak RF. -- "To sum up: The entire structure of antitrust statutes in this country is a jumble of economic irrationality and ignorance. It is a product: (a) of a gross misinterpretation of history, and (b) of rather naïve, and certainly unrealistic, economic theories." Alan Greenspan, "Anti-trust" http://www.ecosystems.net/mgering/antitrust.html Petro::E-Commerce Adminstrator::Playboy Ent. Inc.::petro@playboy.com
On Thu, Nov 05, 1998 at 12:11:20AM -0600, Jim Choate wrote:
It depends on the frequency. Last time I checked a laser or a maser (both are radio waves strictly speaking) travel LOS. The scattering comes from beam divergence and incidental refractions and reflections from the molecules in the air and supported detritus.
Lasers are a technology for generating light, not kinds of radio waves. And masers are a fairly obscure technology for amplifiying weak microwave signals in cryogenicly cooled devices. Both deal with electomagnetic radiation and obey Maxwells laws ....
Microwave ovens work by having the waves bounce around inside a box. Any significant hole or crack (up to roughly half the wavelength) would let the waves out.
Depends on the size of the hole and location. In most microwave ovens there are definite dead-spots (corners and the exact center of the area are notorius).
Most microwave ovens incorperate a motorized metallic device called a stirrer that sits directly in the beam of energy from the magnetron and is designed to reflect microwave energy bouncing around the cavity and change the standing wave pattern as it rotates, resulting in much more even distribution of energy. Without the stirrer hots spots would be much worse...
An open top box will not work.
If the microwaves (for example) are transmitted parallel to the open side it might very well work just fine. It's going to depend on a variety of factors that will preclude such a blanket statement from being valid.
Difraction becomes very significant for openings near in scale to the wavelength of the energy in question, thus the edges of the top will act to scatter energy in all directions...
The absolute magnitude isn't really important.
Most of the signals that are emitted by a computer are not in the 100dB dynamic range (@2x=3db that's a signal range of 1:33) , more likely 40-50db if that. For a TTL (5V) signal it barely covers 3dB (LOW is <2.5v and a high is >=4.75). There simply is no way in hell a signal with a 3dB range is going to emit a rf signal that is 100dB.
This makes no sense whatsoever. The EM radiation takes place when changes in the current flowing happen. Thus radiation occurs only when the TTL signal changes state, not during either its high voltage or low volage state. The amplitude of the current step is determined by the impedance of the circuit and how fast the logic switches and how great the voltage or current swing is , and how effectively it gets radiated is determined by the geometry of the conductor and its sourounding ohjects. EM radiation results only from changes in the magnetic and electric fields, not from their steady state values. Thus it is entirely meaningless to talk of the change in steady state values as only "3 db" when no radiation results from either the steady high or steady low value. And indeed near the conductor, the energy radiated from the current step will be 100 db greater than the ambiant (decibels are relative units, thus it is meaningless to talk of "radiating a rf signal that is 100 db"). -- Dave Emery N1PRE, die@die.com DIE Consulting, Weston, Mass. PGP fingerprint = 2047/4D7B08D1 DE 6E E1 CC 1F 1D 96 E2 5D 27 BD B0 24 88 C3 18
participants (4)
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Dave Emery -
Jim Choate -
Petro -
Tim May