🚀 go-pugleaf

fec@cbnewsl.cb.att.com (f.e.carey) writes:

>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?

No, because there is no attempt to place a "mandatory access control"
(MAC) boundary between you and the data. A properly implemented
mandatory access control boundary does not allow software on one side
to write things that are readable on the other. Since the size
information is visible, there isn't a real MAC boundary.

It's also important to distinguish between policy and implementation.
If the policy says "no defect info should be visible to outsiders"
then there's still the issue of whether or not someone seriously tries
to enforce that policy. In your example, the implementation is clearly
inadequate to enforce the specified access control requirement.

>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?

No, because covert channels have to do with electronic transmissions,
particularly ones that don't involve action by an interactive user.

The covert channel concept only makes sense in terms of MAC. Examples
based on conventional operating systems _without_ MAC really don't
work.

Rick.
smith@sctc.com            arden hills, minnesota