[cap-talk] Authority vs. Information Flow

[Karp, Alan H]

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 sounds like "wheat and chaff" that was proposed as an alternative to encryption in the days of export controls (http://people.csail.mit.edu/rivest/Chaffing.txt).  When Alice causes the light to turn on, it's one bit of wheat.  When Dave does, it's one bit of chaff.  Since Bob doesn't have the key (because there isn't one in this case), he cannot do the necessary winnowing.  Hence, although Alice tells something to Bob, he is incapable of "hearing" it.  This example seems to be equivalent to blocking covert channels by preventing wall listening even though you can't prevent wall banging.

________________________
Alan Karp
Principal Scientist
Virus Safe Computing Initiative
Hewlett-Packard Laboratories
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http://www.hpl.hp.com/personal/Alan_Karp