/ Cory Doctorow / 4:13 pm Tue Jun 25, 2013

Snowden spycraft: a fridge is a Faraday cage

NSA leaker Edward Snowden asked journalists who visited him in Hong Kong to put their phones in his room's refrigerator, relying on the fridge's material properties to serve as an inadvertent radio-wave-spoiling Faraday cage.

50

  1. From the article: “A true Faraday cage is a space where radio waves cannot pass and therefore data cannot be transmitted.”

    Well that’s just not true. Data transmission isn’t reliant on radio waves. Even with a totally sealed-off cage (rather than a mesh) you could transmit data via sound.

    1.  you can transmit data via just about anything, but phones DON’T do that. plus sound doesnt get out of a fridge very well.

      1. Travels well enough to tap out some Morse code – that’s all the data transmission you need.

        1. I guess I’ll keep that in mind if I ever need to communicate with someone sitting directly next to a Faraday cage.

  3. I used to work for a small company that got acquired by Cisco. Before they built us a proper cage, we tried using a rolling file cabinet to block out Wi-Fi signals, but they would still leak through. The real cage was made of copper mesh which was grounded by thick wire, and a door that sealed with metal contact to the frame, and was rated to a signal drop of 90dB IIRC.
    I’m guessing a fridge would probably work better than an ungrounded file cabinet. Easy enough to test I guess.

    1. Indeed, this needs to be tested.

      It’s probably not a true Faraday cage, but works well enough at blocking cell phone signals.

    2. I’ve seen cell signals leak through shielded enclosures that were built for the purpose of keeping them out.  But refrigerators seem to have a few things going against them: power cord and condensor coils provide possible paths for signal to leak, even if they weren’t made of plastic (in whole or part) with rubber seals.  

      My guess is the refrigerator primarily defends against eavesdropping on the contents of their conversation.  The phones could have already been tracked to the house.

      1. Yes, it’s quite possible that the refrigerator’s sound-proofing is the more useful factor.

      2. He was staying in a hotel which netizens IDed from a lamp in the background of photographs.

        1. I don’t really get that. My galaxy II S is thin and light — thinner and lighter than an iPhone — and it has a removable battery.

          The real problem, IMO, is illustrated in the linked article:

          In extreme cases when the battery weakens or dies, people can extend a
          phone’s lifespan by swapping in a new battery they bought online or
          elsewhere.

          This may be true for someone who just has to have the latest phone whenever it comes out, but I tend to use technology until it no longer works. My Mp3 player? changed the battery twice so far. My last phone (before the galaxy) I had for about eight years.

          Quotes like the above just bug me. They just assume I, and everyone else, is so heaviliy influenced by marketing that of course we’ll get new phones when the marketers tell us it’s time.

          1. thinner and lighter than an iPhone

            That’s debatable:

            http://www.ubergizmo.com/2011/09/iphone-4-thinner-than-samsung-galaxy-s2-so-says-advertising-standards-authority/

            I tend to use technology until it no longer works

            Once again, you can replace the iPhone battery for 8 bucks and ~20 minutes of your time. It kills the warranty, but by the time you’re doing that, the warranty is already on its way out anyway.

            And, it’s not just about being lighter and thinner…

            More from the article I already linked to in my previous post:

            ” … In fact, when you don’t have to design a product around popping out its battery, you have far more options. Engineers can use batteries in shapes, sizes, and configurations that deliver the requisite charge but are impractical to remove. That, in turn, can allow the industrial designer to create phones with creative contours.
            Motorola certainly agrees. Manipulating the smartphone’s shape and size was its great goal and accomplishment with the Droid Razr; its superskinny superphone measures less than 0.3 inch thick. … ”

            ” … Embedded batteries are also harder to lose and less likely to sustain damage, since there’s usually no door to pop off when you drop the phone. More than that, sealing the back cover means you’re protecting the internals from the elements, which could make the phone more rugged. … ”

            And, once again, back to the point, it’s not just Apple doing it. Many modern Android phones are the same way for various reasons as shown above.

          2. There is obviously something being traded off for consumer battery removability.

            With the iphones, which are obviously not highly optimized for price, that is sure to be mostly size/weight/shape/battery capacity/physical strength.

            Just watch one of those teardown videos of an ipad or iphone and compare with all the infrastructure related to battery removal in your device.

          3. something being traded off for consumer battery removability.

            Once again, it’s trivial to replace the battery on the iPhone. Granted, it’s certainly not nearly as quick as giving it a hatch to remove it from, but it’s not soldered within it either in a deliberate attempt to keep it from being replaced. 8 bucks and 20 minutes isn’t an extreme hurdle to many.

  5. Easy enough to test.  I just made a call and put my phone in the fridge for a while.  Didn’t drop the call.

    Busted.

    I suspect he was just banking on the fridge being relatively soundproof.

      1.  I love that. It’s a physical representation of putting the thought/concept on ice so he doesn’t have to deal with it right away

    2. I’m pretty sure Snowden turned the phones off before putting them in the fridge.  Try replicating that with your test.

      Also, not all fridges are alike.  Some have less metal than others. Also, next time call your phone and let it go to voicemail and stick it in there and see if it can record your voice.

  6. I’d read that a microwave oven works, as it’s whole MO is to contain it’s namesake (and one assumes a fair amount of the rest of the electromagnetic spectrum,) but I reckon folks would balk at putting their gadgets in a microwave over a fridge.  or perhaps he just didn’t get one in his hotel room.  Mr. Schenck raises a great point, the article whiffed the true definition.  but as far as Mr. Snowden was concerned, any port in a storm, eh?

    1. it does attenuate the right frequencies, at least, but i dunno if i’d count on it if the feds were after me. to make a microwave safe you just need to cut out most of the energy, but to get rid of a signal you need to drive it below the noise floor.

      a better idea might be to cut out the protective grilles and turn on a bunch of microwaves to jam the signal. (note: not actually a good idea. do not attempt.)

        1. I thought that those anti-static bags computer parts come in were supposed to work. Just stuck my phone in one and the signal stayed strong.

          2. I was thinking about the old foil trick once cegev mentioned that.  that was something I’d “read somewhere” that actually worked.  and worked, and worked.  man, I was a knucklehead in the 90s.

      3.  My bedroom would appear to work fine, as my phone stops working the minute I put it on the goddamn bedside table…

      4. Huh, that’s interesting. Do you know what band your phone operates in?  1900, 2100, 700mhz, etc.

        When integrating blackberry into my companies network (cellular provider)  I had to run a battery of tests, dropped call, send a text, then go out of coverage, roaming, etc. I used a microwave oven and it worked perfectly. Since they use emr in the microwave band, they are shielded to protect you from it.

        Hmm, an enterprising person would make small farraday cages folks could by and know the bands it blocks……

  7. “Inadvertent” is not right; in this case the properties of the refrigerator were used intentionally. The usual thing is to remove the batteries, though. I imagine that while the signal would indeed be shielded if active phones were placed inside, to some slight extent the enclosure might itself act as antenna, albeit with enormously reduced gain.

  8. I guess if anyone had the intent of eavesdropping he/she wouldn’t rely solely on a cellphone. 

    I heard that a famous Brazilian senator used to have secret meetings in his pool. The “guest” had to strip down and get in the water for a chat.

    1.  Perhaps he just liked to hang out in the pool, surely a long-range directional mike would be useful?

      1. Mansions in Brazil have high fences, unlikely to allow a line of sight for a mike.

        The guy was really a crook (dead now).

  9. When we had problems with interference for one project I worked on, we succeeded in fixing the problem by just wrapping it in more and more aluminium foil. 

    This appears to also work for killing mobile phone signals. A sufficient amount of aluminium foil wrapped around the phone will effectively kill signals. In testing this just now with my Nexus 4 and an area with a strong signal, one square foot of foil, giving around one layer, did not prevent calls or GApps ringing signal, but three square feet, giving around three or four layers, did do so very effectively.

    This seems much easier and much more secure than using a refrigerator, though, as noted, if Snowden was saying this but actually wanted them in the refrigerator to prevent recording, some other method would be needed.

  11. A fridge is a poor Faraday cage, I’m sure he was using it just to block the phones microphone, it doesn’t make any sense to try and block the phones signal when you could block the microphone.

    1. Indeed. Also, no active connection is required for a bug: the reporter is hardly going to leave their phone behind when they depart, and if the phone had been recording everything it could always connect once the reporter has retrieved it, and the phone could then send on its recordings. I’m sure it must have been a way to ensure that no-one was using their phone to record parts of the meeting not agreed to be recorded, or it could even have been a precaution against the fear phones could be hacked to record conversations without their owners’ knowledge or permission.

  14. I don’t remember this being one of le Carré’s “Moscow rules”. Tradecraft has clearly come a long way.

Comments are closed.