  An integral part of safeguarding systems of communicating agents from covert
channel communication is having the ability to identify when a covert channel
may exist in a given system and which agents are more prone to covert channels
than others. In this paper, we propose a formulation of one of the necessary
conditions for the existence of covert channels: the potential for
communication condition. Then, we discuss when the potential for communication
is preserved after the modification of system agents in a potential
communication path. Our approach is based on the mathematical framework of
Communicating Concurrent Kleene Algebra (C2KA). While existing approaches only
consider the potential for communication via shared environments, the approach
proposed in this paper also considers the potential for communication via
external stimuli.
