[mdlug] Curious - Phone Tapping Tech

[Michael Mol]

On Thu, Jun 21, 2012 at 1:53 PM, Aaron Kulkis <akulkis00 at gmail.com> wrote:
> Michael Mol wrote:
>> On Thu, Jun 21, 2012 at 11:21 AM, Robert Adkins II <radkins at impelind.com> wrote:
>>> I am curious to know if phone tapping technology has "caught up" with
>>> Holywood. In terms of being able to take a band and wrap it around a bundle
>>> of phone lines and call that a tapped line.
>>>
>>> I'm curious, because everything that I know regarding this technology
>>> requires that each individual line be physically tapped/connected to in
>>> order to obtain anything.
>>>
>>> I'm talking about Plain Old Telephone Service. Nothing fancy like IP based
>>> or similar.
>>
>> Oh, sure. When I was a kid, I could hear my parents' telephone
>> conversations by picking up the second phone line; it's called
>> crosstalk, and it's a form of accidental inductive coupling.
>>
>> They've probably been making the accidental intentional since WWII.
>>
>
> That's one pair PARALLEL to the other pair, and is an
> entirely different scenario (wrapped AROUND the bundle, and
> therefor, a plane perpendicular to the pair carrying the signal
> to be detected).

I was answering the question of whether snooping is plausible to begin
with, not whether or not a specific technique is plausible.

Yes, if your conductor is parallel to the magnetic field, direct
inductive pickup won't work.

>
>
>> Doing the same thing with a *bundle* of cables would be a bit
>> tricker...but you could probably do a decent job filtering crap out
>> with enough signal processing. Filtering out DSL frequencies to start,
>> then finding any frequency band groups that stop and start (as would
>> happen with a human vocal conversation), and locking in on those.
>> Eventually, you'd need to get a human involved to separate out
>> overlapping conversations.
>>
>> Though, no, I don't expect you could wrap around a bundle of cables
>> and hone in on a specific copper pair.
>
> 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.

-- 
:wq