🚀 go-pugleaf

>I believe this definition intends -- although I see it doesn't state --
>that all system access controls and other security checks are functioning
>correctly.  In other words, process A and process B _are_ obeying all of
>the individual security rules imposed by the system, but somehow process
>A manages to send, and process B to receive, information that the overall
>system security policy would not permit to be sent directly.  (That's why
>its "surprising to the authorities" <1992Aug15.162611.24659@sctc.com> :-)

This is close to my understanding but I don't think 
the covert channel needs to involve communication
between two processes and you don't need a sender
per se.  For example:

If file permission settings prevent me from reading the daily 
files that contains records of production defects in the factory,
the access controls forbiding such access could be
said to be functioning.  Yet if I am able to determine
the size of the files I can infer information about
defect rates.  In such a case there would seem to be
no "sending process". 
Does such a scenario qualify as a covert channel?

Another scenario: If I've being held incommunicado in a
building and denied access to phones, mail, etc. and I am 
able to signal out a message using the venetian blinds, 
Have I utilized a covert channel?

Frank Carey at Bell Labs