[Cryptography] Help investigate cell phone snooping by police nationwide

Jerry Leichter leichter at lrw.com
Sun Jun 8 05:01:19 EDT 2014


On Jun 7, 2014, at 7:56 PM, Bill Cox <waywardgeek at gmail.com> wrote:
> Is there reliable evidence that putting mobiles in a fridge is any
> better illusory comsec than putting pillows around the door also
> comically exhibited to clueless journalists favored by Showman
> Snowden? Or at least as tall-taled by comical Glenn.
> It's called a Faraday cage.  I'd test it right now, but I think someone hid my mobile phone in a fridge.
The problem is that a refrigerator is not a Faraday cage.  Every refrigerator I've ever used has rubber gasket between the door and the body of the refrigerator.  It's typically 2-3 cm thick.  Cell phone wavelengths vary with band, but range from somewhere around 30 cm down to around 8 cm.  A refrigerator should attenuate the signal, probably quite a bit, but it's not going to block completely.

Of course, this assumes that the point of the exercise is to block the RF.  A refrigerator will also, to some degree, block sounds.  Since nothing inside the food box of a refrigerator typically generates any noise (and of course it's not *sensitive* to noise either), there's no reason to design a refrigerator to be soundproof.  So how much it will muffle outside sounds is unclear.

These things are easy to check experimentally, at least to a good enough approximation to say whether they are likely to be effective for the task at hand.  If it's important to you ... let us know how the experiments come out.

                                                        -- Jerry

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