What is a "communication"

Charles Lindsey chl at clerew.man.ac.uk
Fri Aug 17 12:41:19 BST 2012

On Tue, 14 Aug 2012 03:44:49 +0100, Peter Fairbrother  
<zenadsl6186 at zen.co.uk> wrote:

>> Whether a practical filter could be constructed by a person familiar
>> with the algorithms used by Facebook, or whoever, is a separate
>> issue. For the purposes of this discussion let us assume it is
>> possible.
> Let's take an example, the chalk mark once beloved by fictional spies.
> (aargh, I'm told it was actually often used in real life - well, you
> live and learn).
> Spy Alice places a chalk mark at spot x, and sometime later spy Bob
> passes by the spot and sees it.
> In doing so Bob receives a communication from Alice.
> Now, can "a person familiar with the algorithms used by Facebook, or
> whoever" write a filter to detect that?
> I'm pretty sure he can't, he doesn't have the necessary information, ie
> the placement, the viewing, or the significance of the chalkmark.

How Plod knew how to observe the chalkmark is his secret; "Acting on  
information received" is the usual euphemism. But if he sees it, then he  
has intercepted a communication.

Now maybe the chalk mark is in one of those wartime forts in the Thames  
estuary which is claimed to be extra-territorial, and Plod observes it  
through a telescope on land. Maybe he even has one of those special  
warrants to observe international communications.

The technical details do not matter; if Plod has access to intelligence  
regarding the location, or to a tame geek who knows the Facebook  
algorithms, then he can try to make use of that knwledge. The questions we  
have to address are that, assuming he does possess the necessary  
intelligence somehow, whether or not his subsequent actions amount to  
illegal interception, or not.

Charles H. Lindsey ---------At Home, doing my own thing------------------------
Tel: +44 161 436 6131                       
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Email: chl at clerew.man.ac.uk      Snail: 5 Clerewood Ave, CHEADLE, SK8 3JU, U.K.
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