Resilient Cyber-physical Systems Research Articles

Disaster recovery strategies for cyber-physical systems considering the Interdependence

Improving the resilience of Cyber-Physical Systems (CPS) against extreme events is vital. Current research, overly focused on power system restoration, often misses the complex interplay between the physical and cyber aspects of these systems, leading to potential vulnerabilities. This paper first proposes a framework for CPS considering interdependence. The framework accounts for cyber-physical collaborative recovery and the connectivity between cyber nodes and control center in the cyber system. The model is built considering factors such as repair crew, repair time, and network reconstruction, aimed at rapidly restoring the structural and functional resilience of CPS in the shortest possible time. Next, it integrates complex network theory to propose different repair strategies based on structural and functional indicators. Finally, the repair efficiency of the proposed strategies is comprehensively evaluated using structural and functional metrics. Simulation results show that the repair efficiency of CPS is superior to traditional power grids, and moderate reduction in the repair time of cyber nodes and a decrease in network size both contribute to enhancing repair efficiency.

Designing Secure and Resilient Cyber-Physical Systems: a Model-based Moving Target Defense Approach

Designing Secure and Resilient Cyber-Physical Systems: a Model-based Moving Target Defense Approach

Enforcing Resilience in Cyber-physical Systems via Equilibrium Verification at Runtime

Cyber-physical systems often operate in dynamic environments where unexpected events should be managed while guaranteeing acceptable behavior. Providing comprehensive evidence of their dependability under change represents a major open challenge. In this article, we exploit the notion of equilibrium, that is, the ability of the system to maintain an acceptable behavior within its multidimensional viability zone and propose RUNE 2 (RUNtime Equilibrium verification and Enforcement), an approach able to verify at runtime the equilibrium condition and to enforce the system to stay in its viability zone. RUNE 2 includes (i) a system specification that takes into account the uncertainties related to partial knowledge and possible changes; (ii) the computation of the equilibrium condition to define the boundaries of the viability zone; (iii) a runtime equilibrium verification method that leverages Bayesian inference to reason about the ability of the system to remain viable; and (iv) a resilience enforcement mechanism that exploits the posterior knowledge to steer the execution of the system inside the viability zone. We demonstrate both benefits and costs of the proposed approach by conducting an empirical evaluation using two case studies and 24 systems synthetically generated from pseudo-random models with increasing structural complexity.

A Timing-Based Framework for Designing Resilient Cyber-Physical Systems under Safety Constraint

Cyber-physical systems (CPS) are required to satisfy safety constraints in various application domains such as robotics, industrial manufacturing systems, and power systems. Faults and cyber attacks have been shown to cause safety violations, which can damage the system and endanger human lives. Resilient architectures have been proposed to ensure safety of CPS under such faults and attacks via methodologies including redundancy and restarting from safe operating conditions. The existing resilient architectures for CPS utilize different mechanisms to guarantee safety, and currently, there is no common framework to compare them. Moreover, the analysis and design undertaken for CPS employing one architecture is not readily extendable to another. In this article, we propose a timing-based framework for CPS employing various resilient architectures and develop a common methodology for safety analysis and computation of control policies and design parameters. Using the insight that the cyber subsystem operates in one out of a finite number of statuses, we first develop a hybrid system model that captures CPS adopting any of these architectures. Based on the hybrid system, we formulate the problem of joint computation of control policies and associated timing parameters for CPS to satisfy a given safety constraint and derive sufficient conditions for the solution. Utilizing the derived conditions, we provide an algorithm to compute control policies and timing parameters relevant to the employed architecture. We also note that our solution can be applied to a wide class of CPS with polynomial dynamics and also allows incorporation of new architectures. We verify our proposed framework by performing a case study on adaptive cruise control of vehicles.

Developing Resilient Cyber-Physical Systems: A Review of State-of-the-Art Malware Detection Approaches, Gaps, and Future Directions

Cyber-physical systems (CPSes) are rapidly evolving in critical infrastructure (CI) domains such as smart grid, healthcare, the military, and telecommunication. These systems are continually threatened by malicious software (malware) attacks by adversaries due to their improvised tactics and attack methods. A minor configuration change in a CPS through malware has devastating effects, which the world has seen in Stuxnet, BlackEnergy, Industroyer, and Triton. This paper is a comprehensive review of malware analysis practices currently being used and their limitations and efficacy in securing CPSes. Using well-known real-world incidents, we have covered the significant impacts when a CPS is compromised. In particular, we have prepared exhaustive hypothetical scenarios to discuss the implications of false positives on CPSes. To improve the security of critical systems, we believe that nature-inspired metaheuristic algorithms can effectively counter the overwhelming malware threats geared toward CPSes. However, our detailed review shows that these algorithms have not been adapted to their full potential to counter malicious software. Finally, the gaps identified through this research have led us to propose future research directions using nature-inspired algorithms that would help in bringing optimization by reducing false positives, thereby increasing the security of such systems.

Guest editorial: Application of cloud energy storage systems in power systems

Guest editorial: Application of cloud energy storage systems in power systems

Resilience analysis of cyber-physical systems: A review of models and methods.

Cyber-physical systems (CPSs) are monitored and controlled by a computing and communicating core. This cyber layer enables better management of the controlled subsystem, but it also introduces threats to the security and protection of CPSs, as demonstrated by recent cyberattacks. The resulting governance and policy emphasis on cybersecurity is reflected in the academia by a vast body of literature. In this article, we systematize existing knowledge on CPS analysis. Specifically, we focus on the quantitative assessment of CPSs before and after the occurrence of a disruption. Through the systematic analysis of the models and methods adopted in the literature, we develop a CPS resilience assessment framework consisting of three steps, namely, (1) CPS description, (2) disruption scenario identification, and (3) resilience strategy selection. For each step of the framework, we suggest established methods for CPS analysis and suggest four criteria for method selection. The framework proposes a standardized workflow to assess the resilience of CPSs before and after the occurrence of a disruption. The application of the proposed framework is exemplified with reference to a power substation and associated communication network.The case study shows that the proposed framework supports resilience decision making by quantifying the effects of the implementation of resiliencestrategies.

Cyber-Physical Integration for Future Green Seaports: Challenges, State of the Art and Future Prospects

To achieve the “carbon neutrality” target, multiple heterogeneous energy networks are integrated within seaport areas to form a special energy system with tight “transportation-energy” coupling, which brings massive information exchanges between different networks and therefore motivates the cyber-physical integration of seaports. This paper first summarizes the activity clusters and the promising technologies for future green seaports. After that, the cyber-physical integration framework within seaport area is promoted and the typical operating strategies are overviewed. Then the physical models of seaport are provided with a solid literature survey. At last, this paper proposes three key problems for the cyber-physical integration within seaport areas: the hybrid cyber-physical model in seaport, the economy of cyber-physical system in seaport and the resilience of cyber-physical system in seaport.

A Novel Framework for the Design of Resilient Cyber-Physical Systems Using Control Theory and Formal Methods

A Novel Framework for the Design of Resilient Cyber-Physical Systems Using Control Theory and Formal Methods

Resilience of Cyber-Physical Systems: Role of AI, Digital Twins, and Edge Computing

Cyber-physical systems encompass multiple system domains (i.e., water, energy, networking) with heterogeneous goals and complexity of interactions. Existing technologies do not address the disparate time and spatial scales across the many system domains, especially with the latest threats and challenge spaces. New methods to manage resilience of systems, including integrating new computing and sensing strategies, machine learning and artificial intelligence, as well as advanced resilience analytics and prediction, are required to ensure that cyber-physical systems can withstand adverse events. This article summarizes the results of the December 2021 Society for Risk Analysis “Workshop on Resilience Analytics: Methodology and Applications to Cyber-Energy Systems” in which a multidisciplinary team of researchers, policymakers, military, and industry professionals met to identify priorities for research.

Resilient energy management incorporating energy storage system and network reconfiguration: A framework of cyber‐physical system

AbstractDue to increasing the intricacies of cyber‐physical systems (CPSs) and the severity of natural phenomena, upgrading network planning is vital to reduce the vulnerability of these systems. This study develops a novel preventive‐corrective resilient energy management strategy (PC‐REMS) for a CPS in two stages, exploiting the network reconfiguration (NR) and energy storage systems (ESSs) capacity. The first stage of the proposed PC‐REMS follows preventive actions based on contingency faults. In contrast, the second stage applies corrective measures for improving the CPS resilience to cope with natural physical disasters. Vulnerability assessment data is sent to the physical power system daily through the communication network. The first stage of preparing the CPS for predictable faults focuses on pre‐scheduled ESSs and preventive NR to minimise the expected energy curtailment cost. The second stage involves the network recovery in real‐time through corrective NR to minimise energy curtailment cost after the faults. Three resistance, recovery, and resilience indices are introduced for evaluating the effectiveness of the model. The proposed model is examined by performing multiple simulations on the 33 and 118‐bus radial test systems. The simulation results show the efficiency of the proposed PC‐REMS model in dealing with predictable disasters to improve the CPS resilience.

Introduction to the Special Issue on Intelligent Models for Security and Resilience in Cyber Physical Systems

Introduction to the Special Issue on Intelligent Models for Security and Resilience in Cyber Physical Systems

A Survey on Network Security for Cyber–Physical Systems: From Threats to Resilient Design

Cyber-physical systems (CPS) are considered the integration of physical systems in the real world and control software in computing systems. In CPS, the real world and the computing systems are connected through networks with real-time information exchange. The introduction of networking technologies in CPS has substantial advantages in terms of system efficiency, scalability, maintenance, and many more. However, CPS are vulnerable to malicious attackers intruding on the network. The attackers aim to destroy the physical systems with cyber-physical attacks, in which the main objective is to remotely cause malfunctions in physical systems through networks. Therefore, extensive research on cyber-physical security has been conducted to detect cyber-physical attacks and guarantee the stability of the physical systems under cyber-physical attacks. In this survey, we conduct an exhaustive review of the literature on threats to CPS and on resilient CPS design strategies. First, we discuss the structure of CPS, considering physical dynamics, computing systems, and networks. Then, we provide a taxonomy of cyber-physical attacks with three properties (attack space, attack location, and stealthiness). These three attributes represent the requirements for the implementation of cyber-physical attacks. We review existing studies on anomaly-detection strategies against cyber-physical attacks in terms of physics, networks, and machine learning techniques. Moreover, we analyze the impact of typical cyber-physical attacks and the constraints on attack implementations. In particular, for each of the well-established cyber-physical attacks, we present numerical examples that clearly illustrate the time responses of the physical systems with a conventional physics-based anomaly detector. We also review advances in the typical cyber-physical attacks and the detection methods for these attacks. Furthermore, we review resilient CPS designs in the context of control theory, network management, and data-driven technologies. We conclude the survey by identifying future research directions.

Context-Based Resilience in Cyber-Physical Production System

Cyber-physical systems are hybrid networked cyber and engineered physical elements that record data (e.g. using sensors), analyse them using connected services, influence physical processes and interact with human actors using multi-channel interfaces. Examples of CPS interacting with humans in industrial production environments are the so-called cyber-physical production systems (CPPS), where operators supervise the industrial machines, according to the human-in-the-loop paradigm. In this scenario, research challenges for implementing CPPS resilience, promptly reacting to faults, concern: (i) the complex structure of CPPS, which cannot be addressed as a monolithic system, but as a dynamic ecosystem of single CPS interacting and influencing each other; (ii) the volume, velocity and variety of data (Big Data) on which resilience is based, which call for novel methods and techniques to ensure recovery procedures; (iii) the involvement of human factors in these systems. In this paper, we address the design of resilient cyber-physical production systems (R-CPPS) in digital factories by facing these challenges. Specifically, each component of the R-CPPS is modelled as a smart machine, that is, a cyber-physical system equipped with a set of recovery services, a Sensor Data API used to collect sensor data acquired from the physical side for monitoring the component behaviour, and an operator interface for displaying detected anomalous conditions and notifying necessary recovery actions to on-field operators. A context-based mediator, at shop floor level, is in charge of ensuring resilience by gathering data from the CPPS, selecting the proper recovery actions and invoking corresponding recovery services on the target CPS. Finally, data summarisation and relevance evaluation techniques are used for supporting the identification of anomalous conditions in the presence of high volume and velocity of data collected through the Sensor Data API. The approach is validated in a food industry real case study.

On the resilience of modern power systems: A comprehensive review from the cyber-physical perspective

The digital transformation of power systems into cyber-physical systems (CPSs) is the inevitable trend of modern power systems with the integration of large-scale renewable energy. The in-depth interdependence of cyber and physical spaces leads to more complicated external environments for such cyber-physical power systems (CPPSs) and brings great challenges to the resilience of CPPSs. A resilient CPS imposes strict requirements for its ability to cope with high-impact, low-probability cyber-physical disturbances. To better study the vulnerability and resilience of CPPSs, several representative blackouts from the past two decades are reviewed from the cyber-physical perspective. Inspired by general system theory, this study offers a framework with three key features of a CPPS and presents the three-layer interdependences from facilities to functions. The differences between CPPS resilience and conventional power system resilience are also emphasized. Thereafter, the study discusses the influence of cyber-physical disturbances from natural hazards, cyberattacks, and human-in-the-loop on the resilience of CPPSs. Accordingly, a survey of the state-of-the-art resilience-oriented techniques for CPPS in the face of natural hazards is organized based on quantitative metrics as well as planning and operation attributes. Regarding the resilience against cyberattacks, relevant cutting-edge research is reviewed in terms of prevention, detection, and mitigation strategies. Furthermore, from the cyber-physical-social perspective, the exploitation of social behaviors to inform the design of the physical system and the cyber system to ultimately enhance the resilience of CPPSs is also studied. Based on the findings from this research, the remaining challenges and the broad prospects of cyber-physical resilience enhancement techniques are also discussed.

Stochastic model predictive control framework for resilient cyber-physical systems: review and perspectives.

In the era of Industrial 4.0, the next-generation control system regards the cyber-physical system (CPS) as the core ingredient thanks to the comprehensive integration of physical systems, online computation, networking and control. A reliable, stable and resilient CPS should pledge robustness and safety. A significant concern in CPS development arises from security issues since the CPS is vulnerable to physical constraints, ubiquitous uncertainties and malicious cyber attacks. The integration of the stochastic model predictive control (MPC) framework and the resilient mechanism is a possible approach to guarantee robustness in the presence of stochastic uncertainties and enable resilience against cyber attacks. This review paper aims to offer a detailed overview of existing stochastic MPC algorithms and their CPS applications. More specifically, we first review existing stochastic MPC algorithms for both linear and nonlinear systems subject to probabilistic constraints. We then discuss how to extend the stochastic MPC framework to incorporate resilience mechanisms for constrained CPS under various malicious attacks. Finally, we present an architectural stochastic MPC-based framework for resilient CPS and identify future research challenges. This article is part of the theme issue 'Towards symbiotic autonomous systems'.

A resilient hierarchical distributed model of a cyber physical system

ABSTRACT We present a novel modelling scheme to develop a resilient hierarchical distributed model of industrial cyber-physical systems amenable to feedback control. It advances the current research work on cyber-physical system security and resilience by integrating security and self-adaptation features into each of the self-contained units (subsystems) of a cyber-physical system. We compare the proposed modelling scheme with the extant schemes. The proposed scheme is more comprehensive than the extant research work on resilient modelling scheme. The modelling scheme can be used to design resilient cyber-physical systems and build models to assess their security and resilience.

Cyberphysical Security Through Resiliency: A Systems-Centric Approach

Cyber-physical systems (CPS) are often defended in the same manner as information technology (IT) systems -- by using perimeter security. Multiple factors make such defenses insufficient for CPS. Resiliency shows potential in overcoming these shortfalls. Techniques for achieving resilience exist; however, methods and theory for evaluating resilience in CPS are lacking. We argue that such methods and theory should assist stakeholders in deciding where and how to apply design patterns for resilience. Such a problem potentially involves tradeoffs between different objectives and criteria, and such decisions need to be driven by traceable, defensible, repeatable engineering evidence. Multi-criteria resiliency problems require a system-oriented approach that evaluates systems in the presence of threats as well as potential design solutions once vulnerabilities have been identified. We present a systems-oriented view of cyber-physical security, termed Mission Aware, that is based on a holistic understanding of mission goals, system dynamics, and risk.

Review of Design Elements within Power Infrastructure Cyber–Physical Test Beds as Threat Analysis Environments

Cyber–physical systems (CPSs) are an integral part of modern society; thus, enhancing these systems’ reliability and resilience is paramount. Cyber–physical testbeds (CPTs) are a safe way to test and explore the interplay between the cyber and physical domains and to cost-effectively enhance the reliability and resilience of CPSs. Here a review of CPT elements, broken down into physical components (simulators, emulators, and physical hardware), soft components (communication protocols, network timing protocols), and user interfaces (visualization-dashboard design considerations) is presented. Various methods used to validate CPS performance are reviewed and evaluated for potential applications in CPT performance validation. Last, initial simulated results for a CPT design, based on the IEEE 33 bus system, are presented, along with a brief discussion on how model-based testing and fault–injection-based testing (using scaling and ramp-type attacks) may be used to help validate CPT performance.

Stealthy Sensor Attack Detection and Real-Time Performance Recovery for Resilient CPS

Cyber-physical attacks exploit intrinsic natures of physical systems and can severely damage cyber-physical systems (CPSs) without being detected by the conventional anomaly detector. In this article, based on software-defined networking, we propose a holistic resilient CPS framework that can detect, isolate, and recover from cyber-physical attacks in real time. To show the effectiveness of the proposed framework, we focus on the pole-dynamics attack (PDA), a newly reported stealthy sensor attack that can make the physical system unstable. We develop an efficient detection algorithm for PDA and embed it into the proposed framework. By implementing a testbed, we validate that the proposed framework guarantees resilience of CPS against the PDA.