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."

UK defense system

[legoburner]

BAE in the UK [silicon.com] 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.

Leaky

[QuantumFTL]

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 :)

Sheet rock

[diablovision]

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....

Re:What about windows?

[ScrewMaster]

... which would need to be covered in a mesh in order to make the whole building a farady cage.

Not necessarily. I would imagine that some kind of transparent conductive coating could be sprayed onto the glass, and reapplied periodically. For example, my car's windshield has a conductive layer that is used as the radio antenna (it also inconveniently blocks my tollway transponder, something I did not foresee when I ordered the thing.) I'm sure that there would be plenty of window manufacturers that would be happy to sandwich a clear conductive layer in their products were there a demand for this.

Yeah, you're right it's not that hard to provide a decently secure wireless setup ... but a whole heck of a lot of businesses don't seem to have a clue how to do it. And even if they have an efficient IT department, there's always the idiot that jacks a WRT54G into his office Ethernet port and sticks it under his desk. A giant Faraday cage would provide at least some protection against external snooping and user stupidity. There was an article posted here on Slashdot a while ago about a couple of guys that built a shotgun antenna and went couch-fishing for bluetooth signals in office buildings. They picked up a whole lot of things that they shouldn't have been able to.

We have a Faraday caged room

[digitalderbs]

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.

shielded windows and wallets

[gsn]

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.

Why does it have to be a physical?

[DoubleRing]

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.

Re:The truth may be out there...

[arivanov]

It does not need to be a tin hat.

Our office has IR tempered glass (which is quite common in "all-glass" buildings nowdays.

Stops WiFi dead in its tracks. The signal drops by 20+db when going outside the building to the point where you can no longer home in with a normal receiver. Granted, this will not help against a professional attacker, but it is more then enough against random wardriving k1dd10tz.

So if you have to chose between two buildings which are all-glass and glass windows + wall for a new office the all-glass is better as far as WiFi is concerned. Wardrivers aside, allocating channels without worrying about neighbours is quite a nice thing to have.

Re:UK defense system

[macemoneta]

My parents established an RF shield on our home back in the 1960s. Of course, back then it was called foil and flock wallpaper and it was quite hideous. It still was an effective RF shield. It also made a dandy electrical conductor as I found out, when a foil edge made contact to the hot in an outlet. Something to keep in mind as you RF shield your buildings.

Re:Faraday Cages will work

[budgenator]

The missile I worked on had thin gold wires embeded into the parabolic reflector at 1/4 wavelength intervals so that it would only reflect the frequency we used, as an anti-jamming measure. They could block a WIFI frequency and very little else, I suspect a 2.4GHz cordless phone wouldn't penetrate, but a cell phone in the 900MHz range might not be affected at all.

Inadvertent Faraday Cages

[Randseed]

A certain major medical center in the United States which was built in the late 1960s acts as a Faraday cage "by accident," much to the supreme annoyance of everyone involved. Basically, for whatever reason, when they built the building, they used some chicken-wire-like material that's at just the right dimensions to block 2.4GHz wireless transmissions. They didn't do it consistently, either, because they never thought of this. As a result, there are places where cell phones are Faraday-caged-out, places where WiFi works through an internal wall next to places where it doesn't, and so on. It's such a huge pain in the ass that they've had to put about three times the wireless access points that they otherwise would need to, and they still have dead places.

So yes, it does work.

why is everybody so concerned about wireless secur

[schweini]

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?

20 db drop is not always enough.

[Anonymous Coward]

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.

Not just WiFi

[Beryllium Sphere(tm)]

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.