Concealability Analysis for Current-State Opacity Enforcement via Editing Functions

This paper focuses on the problem of enforcing current-state opacity of a discrete event system via editing functions. In more detail, the observation exposed to an intruder is modified, either erasing or inserting some observations, so as to guarantee that the intruder is not able to discover the predefined secret. The notion of concealability, which formalizes the possibility of maintaining the secret hidden, is introduced starting from defining some illegal states on a particular structure called joint observer. An algorithm for the analysis of concealability is proposed. Finally, an online procedure to make the system opaque is proposed by selecting an editing function.