  This work investigates the problem of synthesizing fortified supervisors
against covert actuator attackers. For a non-resilient supervisor S, i.e.,
there exists at least a covert actuator attacker that is capable of inflicting
damage w.r.t S, a fortified supervisor S' satisfies two requirements: 1) S' is
resilient against any covert actuator attacker, and 2) the original
closed-behavior of the closed-loop system under S is preserved, that is, S' is
control equivalent to S. By designing a sound and complete procedure, we show
the problem of determining the existence of a fortified supervisor against
covert actuator attackers is decidable. We also discuss how to extend the
decidability result to the case against the worst-case attacker.
