Enforcing current-state opacity through shuffle in event observations

摘要

Opacity is a property that ensures that a secret behavior of the system is kept hidden from an Intruder. In this paper, we deal with current-state opacity, and propose an Opacity-Enforcer that is able to change, in an appropriate way, the order of observation in the event occurrences in the system, so as to mislead the Intruder to wrongly estimate estimate at least one non-secret state. A necessary and sufficient condition for the feasibility of the Opacity-Enforcer synthesis is presented and also two algorithms to build the automaton that realizes such an enforcement. An example taken from the literature is used to illustrate the results of the paper.