[cap-talk] Authority vs. Information Flow

[Toby Murray]

On Wed, 2008-02-13 at 13:30 -0500, Jack Lloyd wrote:
> On Wed, Feb 13, 2008 at 04:19:23PM +0000, Toby Murray wrote:
> 
> > Both Alice and Dave now have authority to cause Bob to be able to see
> > the light turn on. But can either of them pass information to Bob?
> > 
> > This question seems tricky because when Bob sees the light turn on, he
> > can't know for sure who turned it on (Alice or Dave). Hence, it seems
> > possible to argue that neither can pass information to Bob.
> 
> Consider an iterated example, where both Dave and Alice can turn the
> light on or off at any time - then the usual channel coding mechanisms
> can be applied. How fast they could communicate would depend on how
> 'noisy' Dave was (for instance if he never touches it, compared to him
> flipping the light on and off constantly), but it seems it would
> always be possible for Alice to send information to Bob at some
> non-zero rate (if perhaps very small). If Dave and Alice are working
> in concert, then they could even both transmit to Bob without
> interfering with the other (ala Ethernet or TDMA), for instance by
> Alice signalling on every odd second and Dave signalling every even
> one.
> 

I tend to agree now that I've thought about it. Thanks.

> I think you could make a reasonable analogy between your situation and
> covert channels.

I'm interested in determining when one object/subject can pass
information to another via overt channels in the first instance. In
particular, when one has the authority to (indirectly) influence the
second (via overt channels -- i.e. through use of its permissions) and
whether or not this always corresponds to an ability to pass
information.


> 
> -Jack
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