[Cryptography] Help investigate cell phone snooping by police nationwide

[Sidney Markowitz]

On Sat, Jun 7, 2014 at 8:02 AM, John Young <jya at pipeline.com
> <mailto:jya at pipeline.com>> wrote:
>     Is there reliable evidence that putting mobiles in a fridge is any
>     better illusory comsec than putting pillows around the door also
[...]
Bill Cox wrote, On 8/06/14 11:56 am:
> It's called a Faraday cage.  I'd test it right now, but I think someone hid my
> mobile phone in a fridge.

Did Snowden say it was because a fridge is a Faraday cage or was that
explanation only from reporters discussing the meeting?

The test is easy and disproves the idea, as demonstrated in these two links:

http://mentalfloss.com/article/51597/does-refrigerator-make-good-faraday-cage

http://makezine.com/2013/06/26/edward-snowden-can-a-refrigerator-function-as-a-faraday-cage/

A microwave oven is a better choice, as it is designed to function as a
Faraday cage.

However, might not the audio insulation and the hum of the refrigerator motor
when the phone is inside the refrigerator in another room be sufficient to
mask the conversation?

I did some Googling about that. According to Table 1 in

http://www.iiav.org/archives_icsv/2009_icsv16/content/technical_papers/377.pdf

the approximate sound insulation of a modern refrigerator varies by frequency,
with the lowest amount in the voice frequency range being about 13dB. The
sound from the fan is about 30dB.

According to

http://www.engineeringtoolbox.com/voice-level-d_938.html

normal conversational voice levels at a distance of 12 feet (3.7m) would be 48dB.

I'm not sure from the literature I've seen how much dB loss to allow for there
being a wall and closed door between the room the meeting is in and the
kitchen. Maybe 30dB for a typical non-insulated interior wall rated at STC 33?
I think that means that there could be up to 5dB of sound energy at the worst
frequencies making it to the inside of the refrigerator, and 30dB of hum from
the fan. If there are two walls, and/or at least 5m distance between the
meeting and the refrigerator that should be enough.

I don't know what would make me feel safer - putting the phones in a microwave
oven with the chance that the door could easily be left ajar, or getting the
acoustic insulation and masking hum of a refrigerator.

 Sidney Markowitz
 http:/sidney.com