Cybersecurity of discrete event systems (DES) has been gaining more and more
attention recently, due to its high relevance to the so-called 4th industrial
revolution that heavily relies on data communication among networked systems.
One key challenge is how to ensure system resilience to sensor and/or actuator
attacks, which may tamper data integrity and service availability. In this
paper we focus on some key decidability issues related to smart sensor attacks.
We first present a sufficient and necessary condition that ensures the
existence of a smart sensor attack, which reveals a novel demand-supply
relationship between an attacker and a controlled plant, represented as a set
of risky pairs. Each risky pair consists of a damage string desired by the
attacker and an observable sequence feasible in the supervisor such that the
latter induces a sequence of control patterns, which allows the damage string
to happen. It turns out that each risky pair can induce a smart weak sensor
attack. Next, we show that, when the plant, supervisor and damage language are
regular, it is computationally feasible to remove all such risky pairs from the
plant behaviour, via a genuine encoding scheme, upon which we are able to
establish our key result that the existence of a nonblocking supervisor
resilient to smart sensor attacks is decidable. To the best of our knowledge,
this is the first result of its kind in the DES literature on cyber attacks.
The proposed decision process renders a specific synthesis procedure that
guarantees to compute a resilient supervisor whenever it exists, which so far
has not been achieved in the literature.Comment: 14 pages, 11 figure