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Can Faraday Cages Tame Wi-Fi?
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."
So this is essentially a giant tinfoil hat for your office? Will it stop the voices as well?
While adding a thin mesh around the building might not be hard to do at construction time, it seems the author has ignored windows. Most larger commercial buildings have large windows, which would need to be covered in a mesh in order to make the whole building a farady cage. This would obviously seriously impact the building's appearance, and I doubt would ever become practical. It's not that difficult to set up a WPA2 or VPN setup if you're concerned about keeping wifi secure.
BAE in the UK have made a wallpaper to do just this. No word on if it is available to consumers though I bet there is a market in the paranoid EM fearing folk that live near 'evil' cell phone masts.
Warhammer forums
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.
I'm sure this will help minimize effects of leakage, but no building can have a "perfect" faraday cage on standard wifi frequencies - the wavelengths are far smaller than the openings required for humans to enter and exit the building.
:)
Once again, it's probably better to focus on good encryption, though this is hardly much help to defeat certain on-site DOS attacks. Then again, that's what your security force is for
After succeeding in preventing the wi-fi signal from "leaking", you are surprised your cellphone stopped working.
^_^
The best wireless security solution is just to not use wireless. Yes, it's sexy. Yes, I know it can be a pain when there's a split in an ethernet cable that's in the rafters. Yes, I like to be able to use this laptop on the couch because it helps my creative energies get flowing. But seriously, if I were at all concerned about security, I'd just stick at CAT5E into the side and be done with it. Big wireless deployments are things for college students and people who like cafes. If I were running a business, I wouldn't throw money at a wireless project to begin with, let alone build an elaborate jamming/shielding system to correct problems which could've been avoided by not doing anything in the first place.
So we can replace the wires from each user to a building-wide mesh of wires.
The cheapest way to do this would probably be to embed a mesh into the sheet rock. The manufacturer of the sheet rock could do this in their factory; you'd just select the "faraday sheet rock" model when remodelling. No extra labor costs, which, after all, is the biggest part of construction.
Still probably going to be rather expensive, it being a whole "chicken and egg" type of situation.
It's probably cheaper on the whole to use good wireless security and regularly test for employees opening unsecured wireless networks using some workstations with wifi cards running shell scripts looking for unsecured networks....
120 characters isn't enough to explain it.
A long time ago, I was a contractor for an establishment whose headquarters was over 4 city blocks and >10 stories above. The building was constructed entirely as a Faraday Cage (nothing inside got outside, checked on a regular basis). When the building was first constructed, the contractor adhered the wire mesh (windows were already shielded) with standard galvanized nails (inside receptor/conductor through shielding/outside transmitter). Go figure...
And ye shall know the truth, and the truth shall make you free.
John 8:32(King James Version)
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.
In my research lab, we have a Faraday caged room with dimensions of about 35feet x 50feet x 30feet. We house 3 NMR spectrometers there, and use the cage to shield us from stray RF from radio stations and other sources. (The lab is in NYC, and as you can imagine, there's a lot of EM noise).
The system works quite well, but we still get quite a bit of leakage through the two doorways (they have a copper lining as well). We can still pickup cell phone calls within 3-4 feet of the doorway (when closed), but not much more than that. However, the room is quite dead for WiFi transmission.
There shouldn't be a problem if you had unshielded windows as long as long as we are not talking about a building with all glass on one side. The Faraday cage wil shield pretty effectively even if there are some gaps. This is why you can get away with using a mesh rather than putting everything inside solid metal boxes. If you've even seen the lightning demos with people in cages being completely unaffected while a big Van de Graff shoots sparks around the place (MOS in Boston has this - its fun).
This seems like its overkill - be more sensible to have some encryption and maybe a system where you have to login to get access to the web is more practical. This way you get to keep what few bars you have on the cell.
With respect to the RFID in passports or on cards, yeah you might want a Faraday cage in your wallet but I wonder how long it is before that becomes classified as suspicious behaviour. I can just see those TSA officials getting red in the face that you'd dare question their authority by using a shielded wallet and having you detained for an hour - just enough to miss your flight.
Reality must take precedence over public relations, for nature cannot be fooled.
There are so many ways of securing a wireless network without the messy business of placing a mesh wire around the building. The university in the town I live in has a campus wide wireless network. They then use a vpn system (cisco, I believe) to regulate access. Simply, anyone can connect to the wireless network, but you are given no access unless you connect to the university's vpn. Then from there, depending on that account's permissions, you can access the Internet and the university network permissions. I think this system is probably the best ideas because very little additional hardware is required, each account has a separate username/password combination (if the password is compromised, you only are dealing with a single user), and has the added bonus of being able to access the university resources from home. Plus, it works flawlessly with Linux.
Before you die, you see DoubleRing...
A complete faraday cage will contain RF EM waves for the same reason that it will keep EM out.
This is incredible, all this time I thought I just had bad luck. I can't get 1 bar of signal strength on my cell phone, unless I prop the phone against my window and point it at the cell phone tower that I can see ~500' away.
And WiFi? No way! I have 3 access points (One in attic, one in basement, one on the same floor as the PC using it (10' away on the other side of a wall) and do you think I can get a reliable signal? Hell no, but if I am in my car I can pick it up 2 blocks away.
My wifes old 900MHz phone works fine, my new 5.8GHz phone? it'll only work if I stay in the same room as the base-station and the people can only hear me when I yell.
If I try using 802.11a, I get good results (despite my wifes phone and 2 microwave ovens in the house), my CRAP (Completly Ridiculous Assinine Pet) theory is that the lower frequency passes through the super-human drywall that my house is made of. But to compete with that theory I can't understand why a Nerf-ball is able to dent the wall.
Time to move I guess.
"The price good men pay for indifference to public affairs is to be ruled by evil men." ~Plato (427-347 BC)
"Can you hear me now?" No, in fact it will stop your cell phone reception too.
Moderating "-1, Disagree" is simple censorship. Have the guts to post your opinion.
It isn't that hard to stop that kind of thing, actually. Best kind of wire for it: standard ethernet cables. Buy a few switches off of ebay just as everyone else tries going wireless.
I have freaks! I did something right...
So yes, it does work.
did i miss something, or wasn't WPA or WPA2 'secure enough'? i know it's relatively easy to hack wep, but AFAIK, WPA with a good password hasn't been hacked yet? so why do stories about how to block wifi signals at significant cost always pop up now and then?
It depends on how close the road is. 30db gain is allowed legally.
Go past legal and at lot more than 30db can be done.
20 db drop is only good if you network stays under 20db itself. If you fit a 30db arial inside a 20 db shield you shoot self in foot. A farday setup cannot be broken by just fitting a larger arial. But it can block mobile phones. Both ways have a price.
So now the attacker has to come into your foyer and sit around instead of being able to do it from the coffeeshop across the street!
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Police where I live complain that their 800 MHz radios cut out in modern office buildings. Firefighters are in the same band. Think twice before you RF-proof your building.