Concerns for the resilience of Cyber-Physical Systems (CPS)s in critical infrastructure are growing. CPS integrate sensing, computation, control, and networking into physical objects and mission-critical services, connecting traditional infrastructure to internet technologies. While this integration increases service efficiency, it has to face the possibility of new threats posed by the new functionalities. This leads to cyber-threats, such as denial-of-service, modification of data, information leakage, spreading of malware, and many others. Cyber-resilience refers to the ability of a CPS to prepare, absorb, recover, and adapt to the adverse effects associated with cyber-threats, e.g., physical degradation of the CPS performance resulting from a cyber-attack. Cyber-resilience aims at ensuring CPS survival by keeping the core functionalities of the CPS in case of extreme events. The literature on cyber-resilience is rapidly increasing, leading to a broad variety of research works addressing this new topic. In this article, we create a systematization of knowledge about existing scientific efforts of making CPSs cyber-resilient. We systematically survey recent literature addressing cyber-resilience with a focus on techniques that may be used on CPSs. We first provide preliminaries and background on CPSs and threats, and subsequently survey state-of-the-art approaches that have been proposed by recent research work applicable to CPSs. In particular, we aim at differentiating research work from traditional risk management approaches based on the general acceptance that it is unfeasible to prevent and mitigate all possible risks threatening a CPS. We also discuss questions and research challenges, with a focus on the practical aspects of cyber-resilience, such as the use of metrics and evaluation methods as well as testing and validation environments.

翻译：关键基础设施中信息物理系统的弹性问题日益受到关注。信息物理系统将感知、计算、控制与网络通信集成至物理对象及关键任务服务中，使传统基础设施与互联网技术相连接。这种集成虽提升了服务效率，但必须面对新功能带来的潜在威胁。由此引发的网络威胁包括拒绝服务攻击、数据篡改、信息泄露、恶意软件传播等。网络弹性指信息物理系统对网络威胁（例如网络攻击导致系统性能退化）的应对能力——包括预防、吸收、恢复及适应等过程。其目标是确保信息物理系统在极端事件中维持核心功能存续。关于网络弹性的文献快速增长，催生了大量该新兴领域的研究工作。本文系统梳理了信息物理系统网络弹性化建设的现有科学成果。我们系统性调研了近期聚焦网络弹性的文献，特别关注适用于信息物理系统的技术方法。首先阐述信息物理系统及其威胁的基础背景知识，随后综述近年研究中适用于信息物理系统的前沿方法。基于"预防和缓解所有可能威胁不切实际"的普遍共识，我们着重区分传统风险管理方法与现有研究的差异。同时探讨实践层面的网络弹性问题与研究挑战，重点关注度量指标与评估方法的应用，以及测试验证环境等实务环节。