[mdlug] Curious - Phone Tapping Tech

[Michael Mol]

On Thu, Jun 21, 2012 at 2:25 PM, Robert Adkins II <radkins at impelind.com> 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.


> None of which, I presume, is fundamentally easy to accomplish, setup,
> configure and operate for the layman.

A kit to take the output of a hall effect sensor and let you plug a
speaker into it would probably cost around $25 in parts. Active
components would be a hall effect sensor, an op-amp or two for
amplification, and a power regulator. Mass-produced, it could probably
be retailed for $20. It'd be shaped like a wand, with the sensor at
the end, and your headphone jack in the handle.

Operation would involve sticking a couple AA batteries in, plugging in
your headphone and holding the device up against the phone cable. You
could have sold it as a children's toy before everything went
cordless.

-- 
:wq