A Survey of Cyber Attacks on Cyber Physical Systems: Recent Advances and Challenges

A cyber physical system (CPS) is a complex system that integrates sensing, computation, control and networking into physical processes and objects over Internet. It plays a key role in modern industry since it connects physical and cyber worlds. In order to meet ever-changing industrial requirements, its structures and functions are constantly improved. Meanwhile, new security issues have arisen. A ubiquitous problem is the fact that cyber attacks can cause significant damage to industrial systems, and thus has gained increasing attention from researchers and practitioners. This paper presents a survey of state-of-the-art results of cyber attacks on cyber physical systems. First, as typical system models are employed to study these systems, time-driven and event-driven systems are reviewed. Then, recent advances on three types of attacks, i.e., those on availability, integrity, and confidentiality are discussed. In particular, the detailed studies on availability and integrity attacks are introduced from the perspective of attackers and defenders. Namely, both attack and defense strategies are discussed based on different system models. Some challenges and open issues are indicated to guide future research and inspire the further exploration of this increasingly important area.      

Consensus Control of Multi-Agent Systems Using Fault-Estimation-in-the-Loop: Dynamic Event-Triggered Case

The paper develops a novel framework of consensus control with fault-estimation-in-the-loop for multi-agent systems(MASs) in the presence of faults. A dynamic event-triggered protocol(DETP) by adding an auxiliary variable is utilized to improve the utilization of communication resources. First, a novel estimator with a noise bias is put forward to estimate the existed fault and then a consensus controller with fault compensation(FC) is adopted to realize the demand of reliability and safety of a...     

DoS攻击下基于多率采样的多智能体系统安全一致性

本 文 研 究 了 一 类 带 有 多 率 采 样 的 线 性 多 智 能 体 系 统(Multiagent Systems, MASs)在 拒 绝 服务(Denial-of-Service, DoS)攻击下的安全一致性控制问题, 其中DoS攻击通常阻断智能体之间的信息传输. 本文将多率采样在网络化控制系统中的结果推广到了多智能体系统, 并考虑了非理想通信网络环境. 首先, 通过引入一个匹配机制来同步由多率采样引起的智能体不同状态分量的采样数据. 然后, 在DoS攻击下, 针对带有多率采样的线性MAS提出了一个基于多率采样的安全一致性控制器. 通过使用李雅普诺夫稳定性理论和切换系统方法, 获得了包含DoS 攻击持续时间以及攻击频率的安全一致性充分条件. 最后, 给出了一个仿真例子来验证所提方法的有效性, 并给出了多率采样与单率采样机制的性能对比分析.     

Consensus Control of Leader-Following Multi-Agent Systems in Directed Topology With Heterogeneous Disturbances

This paper investigates the consensus problem for linear multi-agent systems with the heterogeneous disturbances generated by the Brown motion.Its main contribution is that a control scheme is designed to achieve the dynamic consensus for the multi-agent systems in directed topology interfered by stochastic noise.In traditional ways,the coupling weights depending on the communication structure are static.A new distributed controller is designed based on Riccati inequalities,while updating the coupling weights associated with the gain matrix by state errors between adjacent agents.By introducing time-varying coupling weights into this novel control law,the state errors between leader and followers asymptotically converge to the minimum value utilizing the local interaction.Through the Lyapunov directed method and It?formula,the stability of the closed-loop system with the proposed control law is analyzed.Two simulation results conducted by the new and traditional schemes are presented to demonstrate the effectiveness and advantage of the developed control method.     

Adaptive Memory Event-Triggered Observer-Based Control for Nonlinear Multi-Agent Systems Under DoS Attacks

This paper investigates the event-triggered security consensus problem for nonlinear multi-agent systems (MASs) under denial-of-service (DoS) attacks over an undirected graph. A novel adaptive memory observer-based anti-disturbance control scheme is presented to improve the observer accuracy by adding a buffer for the system output measurements. Meanwhile, this control scheme can also provide more reasonable control signals when DoS attacks occur. To save network resources, an adaptive memory event-triggered mechanism (AMETM) is also proposed and Zeno behavior is excluded. It is worth mentioning that the AMETM’s updates do not require global information. Then, the observer and controller gains are obtained by using the linear matrix inequality (LMI) technique. Finally, simulation examples show the effectiveness of the proposed control scheme.      

Distributed Adaptive Fault-Tolerant Output Regulation of Heterogeneous Multi-Agent Systems With Coupling Uncertainties and Actuator Faults

In this paper, we consider the distributed adaptive fault-tolerant output regulation problem for heterogeneous multiagent systems with matched system uncertainties and mismatched coupling uncertainties among subsystems under the influence of actuator faults. First, distributed finite-time observers are proposed for all subsystems to observe the state of the exosystem. Then, a novel fault-tolerant controller is designed to compensate for the influence of matched system uncertainties and actuator faults. By using the linear matrix inequality technique, a sufficient condition is provided to guarantee the solvability of the considered problem in the presence of mismatched coupling uncertainties. Moreover, it is shown that the system in closed-loop with the developed controller can achieve output regulation by using the Lyapunov stability theory and cyclic-small-gain theory. Finally, a numerical example is given to illustrate the effectiveness of the obtained result.      

Bipartite Formation Tracking for Multi-Agent Systems Using Fully Distributed Dynamic Edge-Event-Triggered Protocol

In this study, the bipartite time-varying output formation tracking problem for heterogeneous multi-agent systems (MASs) with multiple leaders and switching communication networks is considered. Note that the switching communication networks may be connected or disconnected. To address this problem, a novel reduced-dimensional observer-based fully distributed asynchronous dynamic edge-event-triggered output feedback control protocol is developed, and the Zeno behavior is ruled out. The theoretical analysis gives the admissible switching frequency and switching width under the proposed control protocol. Different from the existing works, the control protocol reduces the dimension of information to be transmitted between neighboring agents. Moreover, since an additional positive internal dynamic variable is introduced into the triggering functions, the control protocol can guarantee a larger inter-event time interval compared with previous results. Finally, a simulation example is given to verify the effectiveness and performance of the theoretical result.      

基于中间观测器的多智能体系统分布式故障估计

针对发生执行器故障的多智能体系统, 论文提出一种新型分布式中间观测器的设计方法, 可以同时估计系统的状态和故障.本文设计的观测器可以应用于严格正实条件和观测器匹配条件不满足的系统.针对多智能体系统的通讯拓扑是有向图和无向图的情况, 分别获得估计误差系统稳定的条件.观测器的参数矩阵可以通过求解线性矩阵不等式(Linear matrix inequality, LMI)计算.针对具有有向拓扑的多智能体系统, 本文方法所需求解的LMI的维数, 等于对单个智能体系统设计观测器所需求解的LMI的维数.这表明应用本文方法进行故障估计时, 计算量不会随着系统中智能体数目的增加而增加.针对多智能体系统通讯拓扑是无向图的情况, 利用Laplacian矩阵的对称性, 可以得到保守性更小的结论.最后, 仿真算例验证了本文方法的有效性.     

信息物理融合系统网络安全综述

信息物理融合系统（cyber-physical systems， CPS）是集计算、通信和控制于一体的智能系统，实现网络和物理的深度协作和有机融合.目前CPS在关键的基础设施、政府机构等领域发挥着越来越重要的作用.由于物理限制，计算机和网络产生的安全漏洞会导致CPS遭受巨大的破坏，同时还会引起经济损失、社会动乱等连锁反应，所以研究CPS的安全问题对于确保系统安全运行具有重要意义.本文结合国内外的研究现状，概述了CPS安全控制和攻击检测的最新进展.首先本文总结了CPS典型的系统建模以满足对系统性能分析的需要.然后介绍了3种典型的网络攻击，即拒绝服务攻击、重放攻击和欺骗攻击.根据检测方法的类别，对CPS攻击检测的发展进行的概述.此外还讨论了系统的安全控制和状态估计.最后总结和展望了CPS网络安全面临的挑战和未来的研究方向.     

工业控制系统安全综述

工业控制系统除了应用于生产制造行业外,还广泛应用于交通、水利和电力等关键基础设施.随着工业数字化、网络化、智能化的推进,许多新技术应用于工业控制系统,提高了工业控制系统的智能化水平,但其也给工业控制系统的安全带来严峻的挑战.因此,工业控制系统的安全倍受研究人员的关注.为了让研究人员系统化地了解目前的研究进展,调研了近3年Web of Science核心数据库、EI数据库和CCF推荐网络与信息安全国际学术会议中发表的与工业控制系统安全相关论文以及其他相关的高水平研究工作.首先,介绍工业控制系统的体系结构及面临的威胁.然后,依据工业控制系统的体系结构,自上而下将其安全研究工作分为ICS-云平台通信安全、HMI-设备通信安全、设备固件安全以及其他安全研究,并从攻击和防御角度进行分析和整理.最后,提出当前工业控制系统安全研究依然面临的主要挑战,并指出未来研究发展的方向.     

Human-in-the-Loop Consensus Control for Nonlinear Multi-Agent Systems With Actuator Faults

This paper considers the human-in-the-loop leader-following consensus control problem of multi-agent systems(MASs)with unknown matched nonlinear functions and actuator faults.It is assumed that a human operator controls the MASs via sending the command signal to a non-autonomous leader which generates the desired trajectory.Moreover,the leader’s input is nonzero and not available to all followers.By using neural networks and fault estimators to approximate unknown nonlinear dynamics and identify the actuator faults,respectively,the neighborhood observer-based neural fault-tolerant controller with dynamic coupling gains is designed.It is proved that the state of each follower can synchronize with the leader’s state under a directed graph and all signals in the closed-loop system are guaranteed to be cooperatively uniformly ultimately bounded.Finally,simulation results are presented for verifying the effectiveness of the proposed control method.     

Theory and Experiments on Enclosing Control of Multi-Agent Systems

This paper proposes a control strategy called enclosing control. This strategy can be described as follows: the followers design their control inputs based on the state information of neighbor agents and move to specified positions. The convex hull formed by these followers contains the leaders. We use the single-integrator model to describe the dynamics of the agents and proposes a continuous-time control protocol and a sampled-data based protocol for multi-agent systems with stationary leaders with fixed network topology. Then the state differential equations are analyzed to obtain the parameter requirements for the system to achieve convergence. Moreover, the conditions achieving enclosing control are established for both protocols. A special enclosing control with no leader located on the convex hull boundary under the protocols is studied, which can effectively prevent enclosing control failures caused by errors in the system. Moreover, several simulations are proposed to validate theoretical results and compare the differences between the three control protocols. Finally, experimental results on the multi-robot platform are provided to verify the feasibility of the protocol in the physical system.      

Distributed Fault-Tolerant Containment Control for Nonlinear Multi-Agent Systems Under Directed Network Topology via Hierarchical Approach

This paper investigates the distributed fault-tolerant containment control(FTCC)problem of nonlinear multi-agent systems(MASs)under a directed network topology.The proposed control framework which is independent on the global information about the communication topology consists of two layers.Different from most existing distributed fault-tolerant control(FTC)protocols where the fault in one agent may propagate over network,the developed control method can eliminate the phenomenon of fault propagation.Based on the hierarchical control strategy,the FTCC problem with a directed graph can be simplified to the distributed containment control of the upper layer and the fault-tolerant tracking control of the lower layer.Finally,simulation results are given to demonstrate the effectiveness of the proposed control protocol.     

多Agent系统中信任和信誉系统研究综述

MAS环境同人类社会类似, 充斥着大量不确定因素,因此,在MAS环境中引入信任来解决合作与交互问题具有重要意义. 信任通常来源于直接信任和信誉两种途径,信誉系统是用于支持信任评价的机制. 信誉系统的研究范围分为个体层和系统层两个层次,信誉系统的研究工作更关注个体层,信任的评价要符合准确性等特点. 信誉系统中信任的表示一般采用基于认知观点和数值观点的方法. 信誉系统采用集中式、分布式和混合式3种体系结构,各种模型都需要明确信任表示、传播与汇总的方法. 目前两个较为成功的分布式多Agent信誉系统是ReGreT和FIRE. 信息不精确的问题是信誉系统中的基本问题,也是一个迫切需要深入研究的课题. 信誉系统研究中的一个突出问题是尚无公认的测试平台,Agent信誉和信任测试床（ART）项目作了有益的探索. 在上述评述的基础上,可以在新模型和机制的构建、现有模型改进和完善、测试平台的研究和开发等方面有待进一步开展工作.     

工业控制系统安全态势感知技术研究

工业控制系统(简称工控)是国家关键基础设施的核心,越来越多的工作开始关注工控系统安全。然而,这些工作的实际应用场景并不统一,因此他们取得的成果无法相互借鉴。为了解决这个问题,在深入研究这些安全技术的基础上,我们提出了工控系统安全态势感知(Situational Awareness for Industrial Control Systems Security, SA-ICSS)框架,该框架由态势觉察、态势理解和态势投射三个阶段构成。在态势觉察阶段,我们首先利用网络测绘和脆弱性发现技术获取完善的目标系统环境要素,如网络拓扑和漏洞信息;其次,我们将入侵检测和入侵诱捕等5种设备部署在目标系统中,以便从控制系统中捕获所有的可疑活动。在态势理解阶段,我们首先基于结构化威胁信息表达(Structured Threat Information Expression,STIX)标准对目标系统进行本体建模,构建了控制任务间的依赖关系以及控制任务与运行设备的映射关系;其次,自动化推理引擎通过学习分析师推理技术,从可疑活动中识别出攻击意图以及目标系统可能受到的影响。在态势投射阶段,我们首先利用攻击图、贝叶斯...     

Adaptive Consensus of Non-Strict Feedback Switched Multi-Agent Systems With Input Saturations

This paper considers the leader-following consensus for a class of nonlinear switched multi-agent systems (MASs) with non-strict feedback forms and input saturations under unknown switching mechanisms. First, in virtue of Gaussian error functions, the saturation nonlinearities are represented by asymmetric saturation models. Second, neural networks are utilized to approximate some unknown packaged functions, and the structural property of Gaussian basis functions is introduced to handle the non-strict feedback terms. Third, by using the backstepping process, a common Lyapunov function is constructed for all the subsystems of the followers. At last, we propose an adaptive consensus protocol, under which the tracking error under arbitrary switching converges to a small neighborhood of the origin. The effectiveness of the proposed protocol is illustrated by a simulation example.      

Group Hybrid Coordination Control of Multi-Agent Systems With Time-Delays and Additive Noises

A new kind of group coordination control problemgroup hybrid coordination control is investigated in this paper.The group hybrid coordination control means that in a whole multi-agent system(MAS) that consists of two subgroups with communications between them,agents in the two subgroups achieve consensus and containment,respectively.For MASs with both time-delays and additive noises,two group control protocols are proposed to solve this problem for the containment-oriented case and consensus-ori...     

一种非线性系统容错控制的混合方法

针对连续搅拌箱式反映器,提出一种闭环非线性系统容错控制的混合方法。即利用“等价偏差”的新概念建立传感器的故障模型,然后基于一种伪偏差分离估计算法,在线得到系统状态和“等价偏差”的估计值。数值仿真结果验证了该方法不仅具有很强的关于传感器故障的容错能力,而且还可检测、分离和估计出相应的故障。     

Resilience Against Replay Attacks: A Distributed Model Predictive Control Scheme for Networked Multi-Agent Systems

In this paper,a resilient distributed control scheme against replay attacks for multi-agent networked systems subject to input and state constraints is proposed.The methodological starting point relies on a smart use of predictive arguments with a twofold aim:1)Promptly detect malicious agent behaviors affecting normal system operations;2)Apply specific control actions,based on predictive ideas,for mitigating as much as possible undesirable domino effects resulting from adversary operations.Specifically,the multi-agent system is topologically described by a leader-follower digraph characterized by a unique leader and set-theoretic receding horizon control ideas are exploited to develop a distributed algorithm capable to instantaneously recognize the attacked agent.Finally,numerical simulations are carried out to show benefits and effectiveness of the proposed approach.     

未知环境中移动机器人故障诊断与容错控制技术综述

以我国月球探测为研究背景,以轮式移动机器人为研究对象,介绍了在外星球表面等未知环境中进行深空探测的移动机器人的故障模型和传感器误差模型,分析了未知环境中移动机器人故障诊断与容错控制的特点.在此基础上综述了国内外在该领域的研究进展和主要方法,包括基于多模型的方法、基于粒子滤波器的方法、基于传感器信息融合的方法以及层次容错结构等. 最后,总结了该领域待解决的几个难点问题,并对该研究领域的发展趋势进行了展望.