Title:   Covert Channels: A close look at one of the necessary conditions for their existence

Software systems contain paths for information transmission that were not intended by their designers. These paths utilize the systems' resources, environment, or established legitimate communication channels. They are called covert channels and can be used as paths to leak out confidential information to unauthorized recipients. To the unwary user, these channels may transport information as if by magic, despite the vigilance of monitors. Because of this, covert channels pose a significant threat to information security. In a system of communicating agents, if there exists a covert channel, then two conditions are satisfied: Constraint on Communication and Potential for Communication. In this talk, we discuss the potential for communication condition. We present a mathematical framework for communication and concurrency called Communicating Concurrent Kleene Algebra (C2KA). C2KA extends the work of Tony Hoare et al. on Concurrent Kleene algebra with the notion of stimuli. Then, we use C2KA to propose a formulation of the potential for communication condition. We discuss the preservation of the potential for communication after the modification of an agent on a communication path.