On Decidability of Existence of Nonblocking Supervisors Resilient to Smart Sensor Attacks

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

Localización de fallas en microredes eléctricas basado en un modelo Markoviano.

The present paper analyzes the effect produced by the appearance of a state or failure event on the system and its environment, component or control structure from the result of algorithms of fault location or FDIs for Electric Microgrids, using a Markovian model. This method will help to understand the propagation of faults and their effect on the Microgrids, in addition to allowing the identification and location of the important faults and its control with fault tolerance techniques. This method not only implements a fault location algorithm, it also achieves a scheme to analyze the fault propagation that occur in Microgrids (MG). For this case, fault locations, the detection of critical points in which a failure can occur, as well as the determination of the most probable route for its propagation, are considered the aim to be resolved. The model was created using the Markov process. It is important to consider that in order for the Markov process to obtain results close to reality, it is necessary to consider not only a model that simulates the dynamic behavior of the system, but also to have more in-depth studies that provide statistical and probabilistic data on failure events, their propagation and decision making once located.El presente trabajo analiza el efecto producido por la aparición de un estado o evento de fallo sobre el sistema y su entorno, componente o estructura de control usando un modelo Markoviano, y a partir del resultado de algoritmos de localización de fallas o FDIs para Microredes Eléctrica. El método ayudará a comprender la propagación de fallas y su efecto en las Micro-redes, permitiendo además identificar y localizar las fallas importantes a tratar y controlar con técnicas de tolerancia a fallas. Este método no solo implementa un algoritmo de localización de falla, además logra un esquema para analizar la propagación de las fallas que se presentan en Micro-redes (MG). Para el caso propuesto, la localización de la falla, la detección de los puntos críticos en los que puede ocurrir una falla, así como la determinación de la ruta más probable para la propagación de las mismas, son considerados como un punto clave a resolver. Es importante considerar que, para que el proceso de Markov obtenga resultados cercanos a la realidad es necesario considerar no solo un modelo que simule el comportamiento dinámico del sistema, también, contar con estudios más profundos que brinden datos estadísticos y probabilísticos de los eventos de fallos, su propagación, y toma de decisiones una vez que estos son localizados

A cyber attack model with bounded sensor reading alterations

One of the major challenges about cyber physical systems is how to prevent cyber attacks to ensure system integrity. There has been a large number of different types of attacks discussed in the modern control and computer science communities. In this paper we aim to investigate one special type of attacks in the discrete-event system framework, where an attacker can arbitrarily alter sensor readings after intercepting them from a target system in order to trick a given supervisor to issue control commands improperly, driving the system to an undesirable state. We first consider the cyber attack problem from an attacker point of view, and formulate an attack with bounded sensor reading alterations (ABSRA) problem. We then show that the supremal (or least restrictive) ABSRA exists and can be synthesized, as long as the plant model and the supervisor model are regular, i.e., representable by finite-state automata.MOE (Min. of Education, S’pore)Accepted versio