-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Sat, 19 Aug 2006 18:49:09 -0500 Bipin Gautam <[EMAIL PROTECTED]> wrote: >Ok, here is something from the book that I was trying to >assemble/write. > >Some Links: http://www.eskimo.com/~joelm/tempest.html >http://www.erikyyy.de/tempest/ > >Lets begin… > >Faraday cages may be used to provide protection from HERF and EMP >effects. > >Countermeasures: >It is easy to defeat ordinary audio eavesdropping, just by >sound-proofing a room. And simply drawing the curtains or creating >a >specially crafted background noise or by using double glass with >air >gap in the middle can soundproof and can defeat newer systems, >which >shine a laser beam onto a glass window and decode any modulation of >the reflected beam caused by sound vibrations in the room. > >Faraday's cage: The charge on a charged conductor resided only on >its >exterior, and had no influence on anything enclosed within it. To >demonstrate this fact he built a room coated with metal foil, and >allowed high-voltage discharges from an electrostatic generator to >strike the outside of the room. He used an electroscope to show >that >there was no electric charge present on the inside of the room's >walls. A Faraday cage is best understood as an approximation to an >ideal hollow conductor. A round drum, sphere etc can act like a >Faraday's Cage. Basically, the enclosure may be made of an unbroken >conducting sheet, like the metal box surrounding a sensitive radio >receiver, or a wire mesh, like that in the door of a microwave >oven. >Any holes in the box or mesh must be significantly smaller than the >wavelength of the radiation that is being kept out, or the >enclosure >will not effectively approximate an unbroken conducting surface. > >This shielding effect is used to eliminate electric fields within a >volume, for example to protect electronic equipment from lightning >strikes and other electrostatic discharges (ESDs). Faraday cages >are >often put to a dual purpose: to block electric fields, as explained >above, and to block electromagnetic radiation. The latter >application >is known as RF shielding. > >Some traditional architectural materials act as Faraday shields in >practice. These include plaster with wire mesh, and rebar concrete. >These will affect the use of cordless phones and wireless networks >inside buildings and houses. While Some buildings have designs that >block radio signals by accident due to thick concrete walls or a >steel >skeleton. >RF and Magnetic shielding: Radio frequency (or RF) shielding is >required when it is necessary to block high frequency - 100 >kilohertz >and above - interference fields. These shields typically use >copper, >aluminum, galvanized steel, or conductive rubber, plastic or >paints. >These materials work at high frequencies by means of their high >conductivity, and little or no magnetic permeability. Magnetic >shields >use their high permeability to attract magnetic fields and divert >the >magnetic energy through them. With proper construction, magnetic >shielding alloys have the ability to function as broadband shields, >shielding both rf and magnetic interference fields. > >Electromagnetic shielding: It is the process of limiting the >coupling >of an electromagnetic field between two locations. Typically it is >applied to enclosures, separating electrical content from the >outside >world, and to cables, separating internal wires from the >environment >the cable runs through. The shielding is achieved using a >conductive >material as a barrier. Typical materials include sheet metal, metal >mesh, ionized gas, plasma and aluminum foil. The shielding can >reduce >the coupling of radio waves, visible light, electromagnetic fields >and >electrostatic fields. The amount of reduction depends very much >upon >the material used, the method of connection of the shield (or >screen) >and the frequency of the fields of interest. One example is a >coaxial >cable, which has electromagnetic shielding in the form of a wire >mesh >surrounding an inner core conductor. The shielding impedes the >escape >of any signal from the core conductor, and also signals from being >added to the core conductor. > >Though i have practically seen putting a dipole near the coaxial >cable >can sniff its signal within despite the sealing. The rf sealing >strict >depends on the quality which i've seen is rare in MOST commercial >products for general uses. > >Shielded Tent: It Shielded enclosures, tempest equipment, shielded >chambers Another way of making sure you are not being bugged is to >use >a shielded tent, which prevents radio waves entering or leaving. >Though Mobile phone calls are impossible from inside the tent, but >no-one will be able to listen to your conversations using bugs or >radio wave listening devices. It will also prevent anyone >intercepting >radio emissions from computers, preventing them from seeing what >you >have on screen. A more sophisticated - and expensive - method is to >build a "clean room", of the type used by the military, to shield >radio waves and electromagnetic signals. > >Wireless Shielding Paint: A company, Force Field Wireless makes >three >products that it says can dramatically reduce the leakage of >wireless >signals from a room or building. The paint contains copper filings >and >an aluminum compound. When spread evenly on a wall, the paint >reflects >signals in frequencies from 100 MHz to 5 GHz. Paint four walls, a >floor, and a ceiling, and you effectively have a Faraday cage, >which >is a specially constructed metal room that blocks all radio >signals in >or out. It also makes copper/aluminum powder that homeowners can >add >to their own paint. The company also makes a window film that cuts >down on signal leakage. This product DefendAir would be an >attractive >option to >protect an RFID-enabled warehouse. >http://news.thomasnet.com/fullstory/459490/3280 > >Critic: Though wireless signals are very hard to completely block. >They will simply radiate over and around obstacles. Metallic paint >might reduce the signal strength, but that's easily compensated >for by >an antenna. Further-more its drawbacks are like it could reduce >cellular reception. Any such technology won't block all signal - it >won't block signal eminating from windows, doors, and screw holes. >What it will do is lower the range from which you can sniff or >connect, with constant equipment, which is plenty to be useful for >some cases. Like a building situated near the center of a military >base. Up to a quarterkilometer away is secured area. But obviously >it >will help you lower the sniffable range of the radiation to >within that security perimeter and it's possible to arrange any >conductive medium to actually amplify RF signals in a given >direction >You are quite likely to find a spot where the signal is >considerably >stronger.
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