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Can Faraday Cages Tame Wi-Fi? 145

Posted by Zonk
from the heeya-heeya-back-wifi-back dept.
mrraven writes "An article at TechWorld discusses the increased need for wireless network security. One possible solution to this problem is the use of building-wide Faraday cages to block the wireless signal from 'leaking'." From the article: "Small installations of RF shielding don't have to be expensive, and the basic concept of a Faraday cage can be extended to all kinds of small everyday objects. Leather wallets sandwiched with a conductive RF-shielding layer can prevent RFID scanners from reading personal information implanted in everything from RFID-enabled access control cards to some credit cards; they're widely available for as little as US$15. For those favoring a more DIY route, several Web sites have information on how to make an RFID-blocking wallet with duct tape and aluminum foil."
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Can Faraday Cages Tame Wi-Fi?

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  • by jmauro (32523) on Saturday August 26, 2006 @02:30PM (#15985503)
    Only if you don't want cell phone coverage or look out side. I work in a building that is EM sheilded using a Faraday cage. It was designed to test new radios so you didn't want outside signals coming in to mess up the test. Needless to say a all-metal no windowless office sucks. You have to go out side to make a cell call and when the AC breaks you're screwed because the place turns into an oven with no windows to open. It's a nice idea, but I doubt most wouldn't like to work in such a place 24-7. I sure don't.
  • by Brett Buck (811747) on Saturday August 26, 2006 @02:47PM (#15985573)
    Window shielding is a well-established technology. Note http://www.lessemf.com/plastic.html [lessemf.com]. This has been done for decades for secure facilities. There's nothing new about RF shielded/Faraday cage buildings.

                Brett
  • by Animats (122034) on Saturday August 26, 2006 @02:53PM (#15985593) Homepage

    Real Faraday cages are an unmitigated pain to deal with. The ones used for RF testing typically have a heavy door, like a walk-in refrigerator, with conductive fingers all around the doorframe that seal against the door. It's not enough to have metal; all the metal has to be connected. And slots will pass a wavelength up to the length of the slot.

    The ones used for high-security classified work are even worse. They're made of welded metal panels. They're a few feet off the ground, so the underside can be checked. Any I/O is fibre optic. Power goes in through huge low-pass filters. Air goes through metal mesh filters. Double doors work like an airlock, and there's a compressed-air system to force the RF-tight door seals. Periodic testing (transmitter inside, receiver outside) insures the tank is really RF-tight.

    Not a fun work environment.

    Painting the walls with conductive paint is a joke.

    There's nothing mysterious about any of this. RF propagation is well understood, and the test gear is easy to obtain. Ask any ham.

  • by Dachannien (617929) on Saturday August 26, 2006 @02:55PM (#15985603)
    Will it stop the voices as well?

    No, but it will keep the voices from using your neighbor's access point.

  • by Bishop (4500) on Saturday August 26, 2006 @03:16PM (#15985667)
    A complete faraday cage will contain RF EM waves for the same reason that it will keep EM out.
  • by JesseL (107722) on Saturday August 26, 2006 @03:44PM (#15985742) Homepage Journal
    A wire screen tends to block EM with a wavlength greater than about twice the size of the holes in the mesh. Since the visible spectrum is in the few hundred nanometer range, and most RF communication happens at wavelengths over 5 centimeters, a screen is a very viable option.
  • by Ivan Matveitch (748164) on Saturday August 26, 2006 @03:47PM (#15985749)
    (a) static configuration: no arp, no dhcp.
    (b) declare an ipsec tunnel from your laptop to your gateway.
    (c) set ipsec policy to require it for all traffic.
    (d) rtfm

            ip link set dev wireless arp off up
            ip address add dev wireless local 192.168.1.2 peer 192.168.1.3
            ip neighbor add dev wireless to 192.168.1.3 lladdr 00:11:24:2c:38:c6 nud permanent

            setkey -c >/dev/null <<-END
                    flush;
                    spdflush;

                    add 192.168.1.2 192.168.1.3 esp 256 -m tunnel
                            -E aes-cbc 0x25d8d1bbcf9b7b416ebd7ce514627539f12dc64e3e75c5a2 0d13277558056a4c
                            -A hmac-sha1 0x17f98a8f668324191ee406855e81130fb17f7726;

                    add 192.168.1.3 192.168.1.2 esp 512 -m tunnel
                            -E aes-cbc 0x25d8d1bbcf9b7b416ebd7ce514627539f12dc64e3e75c5a2 0d13277558056a4c
                            -A hmac-sha1 0x17f98a8f668324191ee406855e81130fb17f7726;

                    spdadd 192.168.1.3 0.0.0.0/0 any -P in ipsec
                            esp/tunnel/192.168.1.3-192.168.1.2/require;

                    spdadd 0.0.0.0/0 192.168.1.3 any -P out ipsec
                            esp/tunnel/192.168.1.2-192.168.1.3/require;
            END
  • by Mr Z (6791) on Saturday August 26, 2006 @03:54PM (#15985763) Homepage Journal

    It's all about the wavelengths. If you want to block ALL EM, then yeah, you need a solid metal enclosure. But, just like you can see into your microwave oven through a wire mesh, you could also put windows on your faraday cage as long as they were covered by an appropriate wire mesh.

    IIRC, the 2.5GHz of a microwave oven beam and the 2.4GHz of WiFi are both around 12 cm wavelength. The holes in the mesh on your microwave are so small that the microwaves can't make it through it without severe attenuation.

    --Joe
  • Can you hear me now? (Score:4, Informative)

    by Spazmania (174582) on Saturday August 26, 2006 @04:20PM (#15985834) Homepage
    "Can you hear me now?" No, in fact it will stop your cell phone reception too.
  • Direct experience... (Score:1, Informative)

    by Anonymous Coward on Saturday August 26, 2006 @04:40PM (#15985885)
    My organization had to build a faraday cage for security requirements around a library about 40 foot squarish. It was enormously expensive to put into place in existing construction, what with pipes, cables, ductwork and whatnot to work around.
    You must remember - people still have to breathe, so air must go in and out easily and in volume.
    I was not directly involved in the installation (I was a user of the library), but IIRC they always had trouble getting it to not leak in some way. Think of RF as high pressure steam - it will always find a leak. Not all RF can be shielded the same way, or the one way that does work is most expensive and hardest.
    I'm sure it can be made to work, if designed into the building from the start, but it's very difficult to add later.
    WiFi is highly likely to be subjected to a lot of industry brainwork figuring out how to sniff it out thru Faraday cages that are supposedly "secure". I suspect a lotta snake oil could be sold this way.
  • by JesseL (107722) on Saturday August 26, 2006 @07:10PM (#15986406) Homepage Journal
    A faraday cage does not need to be conected to an earth ground. In fact a lot of electronic equipment uses the cage/shield its self as a "ground".

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