[mdlug] Curious - Phone Tapping Tech

[Aaron Kulkis]

Michael Mol wrote:
> 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.
> 

That's significantly more sophisticated, and entirely different
geometry than wrapping a wire around a bundle of cables, which
is what Robert asked about.