[Cryptography] "The Visual Microphone: Passive Recovery of Sound from Video"

[Tom Mitchell]

On Mon, Aug 4, 2014 at 9:13 PM, Jerry Leichter <leichter at lrw.com> wrote:

> On Aug 5, 2014, at 12:02 AM, Christian Huitema <huitema at huitema.net>
> wrote:
> > Everything leaks.  Film a bag of chips through a soundproof window,
> decode
>

This makes me wonder more and more what a soundproof wall or window
might be composed of.   With this type of effort the acoustic  attenuation
may need to be astounding and futuresque.

Distance seems to be an issue.  But toss in some synchronous detection
technology bridging the inside data to validate low level external data.
Any numerous set of reflections on a window could  be combined digitally
to the same effect.  Active lasers on glass are not necessary.

Also none mentioned lip reading technology that gets closer to the true data
rate than acoustic sampling.   A fast English speaker talks at something
like
140 wpm which is a lot lower than a couple KHz for "audio" (this is a
transparent window).
As long as it is voice Nyquist limited data rates are not a reflection of
the information
data rates if envelope data can be generated.

Also a camera on an individuals neck, lips, cheeks combined with potato chip
bag data might be used to dig out individual voices.  This could also
qualify the
window and potato chip bag data and improve the ability to listen.

Listening through a window across the way seems very possible if it
is line of sight and can be seen from well out beyond sniper range (miles).
This extends the distance where countermeasures and counter surveillance
might need to exist.

Those responsible for serious secrets have one more thing to lose sleep
over...  ;)   job insecurity...




-- 
  T o m    M i t c h e l l
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