Existence Conditions for Confidentiality in Discrete-Event Systems*

Confidentiality as it has been formulated for discrete-event systems is a way of defining security which allows friendly agents to recover obscured secret information. This work presents two new definitions for confidentiality in discrete-event systems that model the scenario when an adversary is eavesdropping from the beginning of a system's evolution. Necessary and sufficient conditions are also provided for each version of confidentiality that describe the properties a system needs for an encryption function to exist that enforces confidentiality on the system.