Schneier on Security
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December 30, 2004
Wi-Fi Shielding Paint
I have no idea how well this works, but it's a clever idea. From Information Week:
Force Field Wireless makes three products that it says can dramatically reduce the leakage of wireless signals from a room or building.
One odd side-point from the article:
Force Field has been trying to interest the Department of Homeland Security, but discussions are ongoing, Wray says. "Ironically, we have had foreign governments contact us--from the Middle East. Kind of scary." Wray says he won't sell to them.
I wonder what's so scary about selling metal paint to a Middle East government. Maybe the company thinks they will use the paint to "cover up" their misdeeds or poison political prisoners?
Posted on December 30, 2004 at 5:52 PM
• 21 Comments
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A while back The Screensavers on TechTV did a test with this metallic paint. It did cut down the signal, but not to the point were it wasn't radiating from your house.
Further to this, if it cuts down wifi, I'm sure it's cutting out your wireless carriers signal. I'd much rather run ethernet through my house than spend a small fortune on paint reducing my cellular reception.
I just wish everyone who writes about this thing says 'Wireless Shielding Paint' instead 'WiFi Shielding Paint' so that readers can straightaway see why it's useless.
Another good test for lead paint...setup a WAP and see if you can get reception as you move around the house.
Wireless signals are like water. They will simply radiate over and around obstacles. Metallic paint might reduce the signal strength, but that's easily compensated for by an antenna.
I have also heard that military agencies can capture and reconstruct TEMPEST signals up to a distance of 1 km with basic equipment. They found this range while routinely testing their own "secure" (e.g. completely enclosed in metal) facilities for radiation leaks. In contrast to a few coats of metallic paint around large windows and doors, the military was looking for TEMPEST leaks as small as a screw hole.
This sort of paint will, indeed, keep cell-phone signals out exactly as well as it will keep 802.11 signals in -- it works for exactly the same reason that you can't get cell reception inside an elevator. I can see some circumstances where this would be useful. Also, it is possible to design wallpaper that will block specific frequency ranges very effectively, but leave others more or less unscathed.
And yes, of course, this won't block all signal -- it won't block signal eminating from windows, doors, and screwholes. 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. Consider a building situated near the center of a military base. Up to a quarter-kilometer away is secured area. If you lower the sniffable range of the radiation to within that security perimeter, then you're in a lot better position then if the theoritical sniffers could sniff from an anonymous house in the civilian village nearby.
BTW, re doors, paint the door as well, making sure there's decent electrical contact between the wall and the door (such as over the hinges). Not perfect, but better then nothing.
Personally, I'd have more concerns selling it to the Dept. of Homeland security than to a Middle Eastern government... have you ever looked at our own government, like really? Have you? We're f'ing scary!
In the old building I used to work in (built in the late 1940's), when they were trying to deploy a wireless network they ran into huge problems.
Apparently, they were so concerned about the possibility of them working on something classified in the building and having the communists spy on it, they embedded every wall with a fine steel mesh, which destroyed radio and cell phone signal in the building (cell reception was not exactly a concern in the 40's). It also cut the range of 802.11b to within a 1 room distance... making it practically impossible to achieve the goal of "blanket coverage".
They ended up changing the plan for how to give wireless coverage to the building from "everywhere" to "almost nowhere" and ripping out a few walls worth of mesh in key places to hit priority areas. Yesterday's security choices are today's roadblocks.
Like most RF sheilding products this paint can turn out to be more of a liability than a security aid.
It is posible to arange any conductive medium to actually amplify RF signals in a given direction (think old style TV antena), and in buildings this happens more often than not. For example take a VHF portable radio with a signal strength meter around any modern building and note the strength of your favourite radio station. You are quite likley to find a spot where the signal is considerably stronger inside the building than outside especially at ground floor level.
RF sheilding is very difficult to do properly (ask any one who has set up an RF test laboratory) and for those of you who want to know just how hard search on the internet for TEMPEST and have a read.
Back in June, there was an article on silicon.com that claims that BAE Systems in the UK has developed a stealth wallpaper that essentially does the same thing but allows radio and mobile phone frequencies pass through.
I'm not exactly sure how it works or haven't heard anything else about it since the article came out.
Encryption (e.g. IPSec) is a much better idea.
Well… It seems that people at the DHS are smarter than Middle East civil servants. If you consider the price of the FFW “wallpaper��?, you’d better buy 25 yards of aluminium paper at the closest Wall Mart store. It’s far cheaper, and presents approximately the same shielding capabilities… in other words, absolutely none…
Blocking RFI “stray cats��? is a tedious task, every ham radio and electronic designer will confirm you this point. To obtain good RF insulation, you have to cover every window, seal the smallest crack, cover every square inch of floor or ceiling… and plug this faraday cage to a good electrical grounding. The higher the working frequency is, the tougher is the job… SHF (signals over 1 GHz) are like water, the smallest hole means leakage.
If you prefer using the “coating��? solution sold by the very same company, aka the anti-wireless paint, it is cheaper to buy this black paint used to refresh stoves and old ovens (I’ve seen some at Target). This paint is containing a high percentage of pure carbon powder, and is very efficient in all sorts of shielding at very low cost (I use this kind of paint in hyperfrequency attenuators and anechoïd chambers)
I won’t argue anymore about the “other security gadgets��? sold by FFW. The “wifi detector��? is useless compared with simple RFI testers (some of them are called “Microwave oven detectors��? and are sold everywhere for a few bucks). If you need a more elaborate detection device, you can use public domain or free sniffing softwares installed on PDA’s or portable computers: Kismet, WiFifofum, AirSnort, Wepckrack…
By default, never yield to paranoid advertisements made around the wireless world. Most of them can be classified as “bad��? or “useless��? security.
BEA commercialize a “WiFi��? wallpaper using what technicians call “notch��? filters. It is in fact a double side copper/mylar coating engraved with an impressive network of dipoles antennas tuned on peculiar frequencies. This approach is technically efficient, as it blocks only the frequency you wish to control and lets other bands working without problem (for example cell phones or UHF talkies). But the retail price of such a "wallpaper" is very expensive.
At last, I wonder why people would try to block WiFi this way. If you intend to stop any RF radiation from a corporate building, you have to shield the whole place… and multiply the number of Radio Access Point because of the attenuation and unwanted reflexions (bouncing signals) due to the shielding itself. That’s totally unrealistic. If your intend to circumvent RF signals to a very specific room, it could be smarter to use a high end and elaborate technology able to combine security and effectiveness : a 100BaseT copper based cabling system (please, don’t tell others I gave you this info, it’s top secret and brand new)
Sorry for my rotten English… I’ll try to do better next time.
I have read all the comments and I am interested in the possibility of using this Wireless blocking paint for blocking cellular in environments as hospitals, theatres,..ect for all those annoying calls in inappropriate times and places what are a few thoughts on that basic use and/or effectiveness. Any and all comments appreciated.
I am very sensitive to EMF and now find that the signal from my neighbor's wireless router is causing numerous health problems. Please help me - does anyone have a suggestion as to how to block the signal from entering my home??? They could lower the signal strength, but I don't believe they would be sympathetic to my situation. Thanks!
to block the signal , i was told by a commuincations engineer that you would have to encase you house with wire mesh and attach lots of grounding rods going at least 4 foot into the ground . Though i don't see how it would work
Dear Bruce Schneier,
I would appreciate it a lot if you would sell a fully RF shielded box on your website with the back of it providing shielding of the power and video cables in a hollow tube. While on the front of the box it has RF-shielded glass, so that you can just go out and buy whatever type of LCD monitor that you may want. Simply stick it in this box and have a Tempest-equivalent sort of home-brew secure display. This would be like a box that you just stick the monitor inside and there would be shielding also for the cables (much longer than needed) of a flexible material and the entire box would be RF secure. -- a Faraday cage just for your monitor :)
Seriously Mr. Schneier, I would buy this from you. There are plenty of EM shielding companies, but none that offer a simple monitor box that is affordable, that you can stick a monitor inside to make it secure from radiating spurious emissions (TEMPEST leaks).
... And if a glass front that is see-through while also being RF-shielded is not available then you could simply paint the inside of regular glass with an RF shielding paint that is clear. Please *PLEASE* consider my suggestion. If you build it I will buy (and many others as well).
I too cannot take the abundance of wireless signals in my neighborhood. My life is definitely affected with insomnia, and headaches and an incessant buzzing. Neurologist checked me out and gave me a clean bill of health. We are irradiating ourselves. The human race is idiotic.
I shouldn't have said what I did about the human race. I am angry. However, there are well documented cases and studies of ill health effects from the pulsed microwave frequencies of wireless along with other frequencies along the magnetic spectrum. Some of us are getting ill, others are not as aware. Go to bioinitiative.org/report for in depth look.
I Think this is not such a good idea if you are concerned about your health.
This is like using your cell phone in an elevator... radiation has no where to go and its just go right trough your body again and again...
But I think more research is required on this one
Although the Surveilance mad government does bother me, like the guy above i am more concerned about RF radiation being an health risk.
At the moment i am insulating my walls with a kind of Aluminium foil bubble wrap, the main reason for this is, thermal insulation, and the fact that i am getting it at a ridiculously low price.
The bubble wrap is two ply with foil on both sides, we estimate its R-value to be at least 2, we are installing 12 layers in the wall, which should give us at least an R-value of 24, which is fantastic compared to Rockwool and a fraction of the thickness.
But what i am interested in finding out, is just how good this will reduce signals from mobile phone towers ect, i have made alot of effort to earth the sheets of insulation, which is not easy.
Well Barefoot, it's pretty easy to test as nearly all cellphones have a signal strength display right on the screen. Take it inside and see how many bars of signal strength you lose.
As it only takes a single sheet of alfoil to block a signal, lining all your walls with 24 layers (or even one layer, for that matter) will certainly block any signal coming through the walls. However you can still get some coming through the windows, doors, roof (if not metallic), etc. etc.
In any case, I really wouldn't worry about it. The possible health effects have been studied to death and most studies showed no effects at all. True, a couple of studies did show some effects. Given all the negative results it is most likely those were just statistical glitches, but it is clear that even if it is a real effect it is very, very weak -- so weak that it should come about 500th on your list of things to worry about.
It is an ignorant comment posted by Anonymous on May4, 2009: "The possible health effects (cell phone signals) have been studied to death and most studies showed no effects at all." It is alarmingly becoming increasingly evident that cellular/wireless signals are having ill-effects on humans. I could go on for a long time educating the author of that message and the poor readers who are grossly misinformed by having read that as to why this is so. Some key words/concepts: EMF sensitivity, residual effects, cell phones/wireless/wi-fi and electric sensitivity/children, brain cancer and positive correlates with duration and location of cellular phone useage, 40% increase in brain cancer in adult and child populations globally in countries employing cellular technology, inablity to conclusively prove ill effects of EMF d/t varying sensitivity threshholds dependent on prior exposure, residual effects, wireless industries knowledge and exploitation of these facts, wireless industries deliberate manipulation and inconsistency of research design and methodology to refute studies indicating health risk to humans, the health risk of emf to humans was known as studies of emf effects on humans conducted prior to the proliferation of cell phones were terminated due to the danger posed to the subjects...etc...Please DO NOT propagate ignorant comments as to the safety of cellular/wireless technology...If you are going to comment, make sure it is a fully informed comment. Otherwise, you may as well say that lead paint is safe and labotomies are recommended and safe medical procedures. Oh, by the way, the forecast due to proliferate use of such technology is a rapid advance in incidence of Alzheimer's affecting those in their mid-40's, and incidence of electromagnetic sensitivity affecting 50% of global populations using such technology by 2015. Startling and scarey? Yes, it is. Did you know that children are developing sensitivity? What of their future? Respectfully submitted to all readers from an electrosensitive subjected to chronic low dose and brief high dose emf from neighboring tower (both noted for causing sensitivity) who rarely utilized cellular/wireless technology.
Im very concerned with microwave ( cell phone towers etc) radiation and can't believe that some people like "anonymous" makes so uninformed statements. He is obviously reading the wrong research.....the one that industry wants him to read....go and check the real truth abut the research done by Barrie Trower. There was a document written to make sure that all the results of the research are kept secret to protect industrial investment etc.
I also have a question and hope someone can help. I live in an apartment building with the cell tower on it!!! Im about to paint all my walls and ceilings with the shielding paint but can anyone tell me if I also need to cover the floors? I live on 4th level so there are aprtms below me. Am I getting radiation from below? I would really appreciate help with this dillema.
Very concerned citizen
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