Secure State Estimation and Attack Reconstruction in Cyber-Physical Systems: Sliding Mode Observer Approach

Abstract

A cyber-physical system (CPS) is a tight coupling of computational resources, network communication, and physical processes. They are composed of a set of networked components, including sensors, actuators, control processing units, and communication agents that instrument the physical world to make "smarter." However, cyber components are also the source of new, unprecedented vulnerabilities to malicious attacks. In order to protect a CPS from attacks, three security levels of protection, detection, and identification are considered. In this chapter, we will discuss the identification level, i.e., secure state estimation and attack reconstruction of CPS with corrupted states and measurements. Considering different attack plans that may assault the states, sensors, or both of them, different online attack reconstruction approaches are discussed. Fixed-gain and adaptive-gain finite-time convergent observation algorithms, specifically sliding mode observers, are applied to online reconstruction of sensor and state attacks. Next, the corrupted measurements and states are to be cleaned up online in order to stop the attack propagation to the CPS via the control signal. The proposed methodologies are applied to an electric power network, whose states and sensors are under attack. Simulation results illustrate the efficacy of the proposed observers.Keywords: cyber-physical systems, sensor attack, state attack, sliding mode observers Recent real-world cyber-attacks, including multiple power blackouts in Brazil [3], and the Stuxnet attack [4] in 2010, showed the importance of providing security to CPSs. Identification and modeling process as [5,6] which are based on data can be seriously affected by corrupted data. As a result, information security techniques [7] may be not sufficient for protecting systems from sophisticated cyberattacks. It is suggested in [8] that information security mechanisms have to be complemented by specially designed resilient control systems. Controlling CPS with sensors and actuators, who are hijacked/corrupted remotely or physically by the attackers, is a challenge. The use of novel control/observation algorithms is proposed in this chapter for recovering CPS performance online if an attacker penetrates the information security mechanisms.Cyber security of CPS must provide three main security goals: availability, confidentiality, and integrity [7]. This means that the CPS is to be accessible and usable upon demand, the information has to be kept secret from unauthorized users, and the trustworthiness of data has to be guaranteed. Lack of availability, confidentiality, and integrity yields denial of service, disclosure, and deception, respectively. A specific kind of deception attack called a replay attack has been investigated when the system model is unknown to the attackers but they have access to the all sensors [9,10]. Replay attacks are carried out by "hijacking" the sensors, recording the readings for a certain time, and repeating such readings while injecting them together with an exo...

Sliding mode observers for robust fault estimation in linear parameter varying systems

“…The signal 𝜈 in (15) represents a nonlinear injection signal depending on (y 2 − z 22 ) whose purpose is to produce a sliding motion in finite time in the estimation error space. Define the observer gain matrix in (15) associated with 𝜈 as…”

“…5,13,14 Finally the fast developing area of protecting systems against cyber-attacks can also be posed in an unknown input problem framework. 15,16 Because of the engineering applicability of the unknown input reconstruction problem for linear time invariant (LTI) systems, unsurprisingly, a rich collection of different approaches have been developed. For example the ubiquitous (Extended) Kalman filter 17,18 has been used-often involving augmenting the state-space representation with the unknown input signals considered to be states (under the assumption the rate of the change of the unknown input is small).…”

Resilient control of cyber‐physical systems using adaptive super‐twisting observer

“…The state attack line-by-line STWO in Equations ( 25)- (30) discussed in Section 5 suffers from the overestimating the unknown bounds L j i > 0. In this section, it is proposed to replace the line-by-line STWO in Equations ( 25)-( 30) by a gain adaptation algorithm with non-overestimated gains.…”

“…Most of the recent studies on the security of CPSs investigate protection of CPSs to prevent the attacks, detecting the attack, and mitigating the effects of attacks [14][15][16][17][18][19][20][21][22][23][24][25][26]. Quite a few results on the elimination of the effects of attacks have been reported [27][28][29][30][31][32]. In this paper, the objective is to eliminate the destructive effects of attacks, although some considered constraints and assumptions in the recent studies have been removed.…”

“…An approach to protect nonlinear CPS from attack using on-exact reconstruction techniques based on computationally intensive higher order sliding mode (HOSM) differentiator was proposed in literature [27][28][29][30]. They assume that the attacks are bounded with known boundary.…”