Efficient Synthesis of Sensor Deception Attacks Using Observation Equivalence-Based Abstraction

This paper investigates the synthesis of successful sensor deception attack functions in supervisory control using abstraction methods to reduce computational complexity. In sensor deception attacks, an attacker hijacks a subset of the sensors of the plant and feeds incorrect information to the supervisor with the intent on causing damage to the supervised system. The attacker is successful if its attack causes damage to the system and it is not identified by an intrusion detection module. The existence test and the synthesis method of successful sensor deception attack functions are computationally expensive, specifically in partially observed systems. For this reason, we leverage results on abstraction methods to reduce the computational effort in solving these problems. Namely, we introduce an equivalence relation called restricted observation equivalence, that is used to abstract the original system before calculating attack functions. Based on this equivalence relation we prove that the existence of successful attack functions in the abstracted supervised system guarantees the existence of successful attack functions in the unabstracted supervised system and vice versa. Moreover, successful attack functions synthesized from the abstracted system can be exactly mapped to successful attack functions on the unabstracted system, thereby providing a complete solution to the attack synthesis problem

Selection of a stealthy and harmful attack function in discrete event systems

In this paper we consider the problem of joint state estimation under attack in partially-observed discrete event systems. An operator observes the evolution of the plant to evaluate its current states. The attacker may tamper with the sensor readings received by the operator inserting dummy events or erasing real events that have occurred in the plant with the goal of preventing the operator from computing the correct state estimation. An attack function is said to be harmful if the state estimation consistent with the correct observation and the state estimation consistent with the corrupted observation satisfy a given misleading relation. On the basis of an automaton called joint estimator, we show how to compute a supremal stealthy joint subestimator that allows the attacker to remain stealthy, no matter what the future evolution of the plant is. Finally, we show how to select a stealthy and harmful attack function based on such a subestimator

Attack-Resilient Supervisory Control of Discrete-Event Systems

In this work, we study the problem of supervisory control of discrete-event systems (DES) in the presence of attacks that tamper with inputs and outputs of the plant. We consider a very general system setup as we focus on both deterministic and nondeterministic plants that we model as finite state transducers (FSTs); this also covers the conventional approach to modeling DES as deterministic finite automata. Furthermore, we cover a wide class of attacks that can nondeterministically add, remove, or rewrite a sensing and/or actuation word to any word from predefined regular languages, and show how such attacks can be modeled by nondeterministic FSTs; we also present how the use of FSTs facilitates modeling realistic (and very complex) attacks, as well as provides the foundation for design of attack-resilient supervisory controllers. Specifically, we first consider the supervisory control problem for deterministic plants with attacks (i) only on their sensors, (ii) only on their actuators, and (iii) both on their sensors and actuators. For each case, we develop new conditions for controllability in the presence of attacks, as well as synthesizing algorithms to obtain FST-based description of such attack-resilient supervisors. A derived resilient controller provides a set of all safe control words that can keep the plant work desirably even in the presence of corrupted observation and/or if the control words are subjected to actuation attacks. Then, we extend the controllability theorems and the supervisor synthesizing algorithms to nondeterministic plants that satisfy a nonblocking condition. Finally, we illustrate applicability of our methodology on several examples and numerical case-studies

Resilience Against Sensor Deception Attacks at the Supervisory Control Layer of Cyber-Physical Systems: A Discrete Event Systems Approach

Cyber-Physical Systems (CPS) are already ubiquitous in our society and include medical devices, (semi-)autonomous vehicles, and smart grids. However, their security aspects were only recently incorporated into their design process, mainly in response to catastrophic incidents caused by cyber-attacks on CPS. The Stuxnet attack that successfully damaged a nuclear facility, the Maroochy water breach that released millions of gallons of untreated water, the assault on power plants in Brazil that disrupted the distribution of energy in many cities, and the intrusion demonstration that stopped the engine of a 2014 Jeep Cherokee in the middle of a highway are examples of well-publicized cyber-attacks on CPS. There is now a critical need to provide techniques for analyzing the behavior of CPS while under attack and to synthesize attack-resilient CPS. In this dissertation, we address CPS under the influence of an important class of attacks called sensor deception attacks, in which an attacker hijacks sensor readings to inflict damage to CPS. The formalism of regular languages and their finite-state automata representations is used to capture the dynamics of CPS and their attackers, thereby allowing us to leverage the theory of supervisory control of discrete event systems to pose our investigations. First, we focus on developing a supervisory control framework under sensor deception attacks. We focus on two questions: (1) Can we automatically find sensor deception attacks that damage a given CPS? and (2) Can we design a secure-by-construction CPS against sensor deception attacks? Answering these two questions is the main contribution of this dissertation. In the first part of the dissertation, using techniques from the fields of graph games and Markov decision processes, we develop algorithms for synthesizing sensor deception attacks in both qualitative and quantitative settings. Graph games provide the means of synthesizing sensor deception attacks that might damage the given CPS. In a second step, equipped with stochastic information about the CPS, we can leverage Markov decision processes to synthesize attacks with the highest likelihood of damage. In the second part of the dissertation, we tackle the problem of designing secure-by-construction CPS. We provide two different methodologies to design such CPS, in which there exists a trade-off between flexibility on selecting different designs and computational complexity of the methods. The first method is developed based on supervisory control theory, and it provides a computationally efficient way of designing secure CPS. Alternatively, a graph-game method is presented as a second solution for this investigated problem. The graph-game method grants flexible selection of the CPS at the cost of computational complexity. The first method finds one robust supervisor, whereas the second method provides a structure in which all robust supervisors are included. Overall, this dissertation provides a comprehensive set of algorithmic techniques to analyze and mitigate sensor deception attacks at the supervisory layer of cyber-physical control systems.PHDElectrical and Computer EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/166117/1/romulo_1.pd

A Polynomial Approach to Verifying the Existence of a Threatening Sensor Attacker

The development of cyber-physical systems (CPS) has brought much attention of researchers to cyber-attack and cyber-security. A sensor attacker targeting on a supervised discrete event system can modify a set of sensor readings and cause the closed-loop system to reach undesirable states. In this letter, we propose a new attack detection mechanism under which the supervisor only needs to keep track of the last observable event received. Given a plant and a supervisor enforcing a state specification, we define a sensor attacker threatening if it may cause the closed-loop system to enter a forbidden state. Our goal is to verify whether there exists such a threatening sensor attacker for a given controlled system. A new structure, called All Sensor Attack (ASA), is proposed to capture all possible sensor attacks launched by the attacker. Based on the ASA automaton, a necessary and sufficient condition for the existence of a stealthy threatening sensor attacker is presented. Finally, we show that the condition can be verified in polynomial time

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