[mdlug] Curious - Phone Tapping Tech

[Michael Mol]

On Thu, Jun 21, 2012 at 7:02 PM, Aaron Kulkis <akulkis00 at gmail.com> wrote:
> Michael Mol wrote:
>> On Thu, Jun 21, 2012 at 1:53 PM, Aaron Kulkis <akulkis00 at gmail.com> wrote:
>>> Michael Mol wrote:

[snip]

>>> You couldn't detect a signal even if it was only 1 copper pair.
>>> Don't believe me?  Try it.
>>
>> Hall effect sensors would do it easily, in the single-pair case. And
>> if that isn't enough, you could use the signal propagation detection
>> and lock-on technique I wrote about last week to do it. I came up with
>> that in response to the 'thermal noise' encryption thing that was
>> making the rounds last week. It requires three measuring points, and
>> then applies triangulation in a time+distance space to figure out
>> where a signal is coming from and when, and uses that to lock on for
>> pass/block filtering purposes. The hardest part is timecode
>> synchronization between the three measuring points.
>>
>
> That's significantly more sophisticated, and entirely different
> geometry than wrapping a wire around a bundle of cables, which
> is what Robert asked about.

It sounded to me like Robert was asking a question about a real-world
situation where someone was claiming to be able to sniff signal. I was
giving real-world answers. You challenged me on the case of a single
pair. I described how it could be done. I then extended into an
explanation of how one could do it with far more difficult
measurements.

And you tell me my response to you is inapplicable to a misquote of
Robert's case. Perhaps it is...but I wasn't responding to him, there;
I was responding to you.

My first response to Robert sums up my opinion of the situation. Ask
for a demonstration, control the setup; if the guy's a charlatan,
he'll back out. If he's not, he's either going to demo and succeed (in
which case there's something interesting there), or he's going to demo
and be embarrassed. The worst that could happen is a waste of time and
some bruised egos.

If you want to get _really_ sophisticated, take this "band" the guy
was talking about, and build it out of a line of hall effect sensors.
Wrap it around the bundle of cable, and you have something that's
effectively a passive MRI; you've got measurements at the edge of a 2D
space sufficient to build a cross-sectional map of currents going back
and forth within the circle via triangulation. But now we're talking
about something extraordinarily expensive.
-- 
:wq