We address security issues in cyber-physical systems (CPSs). We focus on the detection of attacks against cyber-physical systems. Attacks against these systems shall be handled both in terms of safety and security. Networked-control technologies imposed by industrial standards already cover the safety dimension. However, from a security standpoint, using only cyber information to analyze the security of a cyber-physical system is not enough, since the physical malicious actions that can threaten the correct behavior of the systems are ignored. For this reason, the systems have to be protected from threats to their cyber and physical layers. Some authors have handled replay and integrity attacks using, for example, physical attestation to validate the cyber process and to detect the attacks, or watermark-based detectors which uses also physical parameters to ensure the cyber layers. We reexamine the effectiveness of a stationary watermark-based detector. We show that this approach only detects adversaries that do not attempt to get any knowledge about the system dynamics. We analyze the detection ratio of the original design under the presence of new adversaries that are able to infer the system dynamics and are able to evade the detector with high frequency. We propose a new detection scheme which employs several non-stationary watermarks. We validate the detection efficiency of the new strategy via numeric simulations and via running experiments on a laboratory testbed. Results show that the proposed strategy is able to detect adversaries using non-parametric methods, but it is not equally effective against adversaries using parametric identification methods.

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关于使用基于水印的方案来检测网络物理攻击

我们解决网络物理系统（CPS）中的安全问题。我们专注于检测针对网络物理系统的攻击。对这些系统的攻击应在安全性和安全性两方面进行处理。工业标准施加的网络控制技术已经涵盖了安全方面。但是，从安全角度来看，仅使用网络信息来分析物理网络系统的安全性是不够的，因为可以威胁到系统正确行为的物理恶意行为被忽略了。因此，必须保护系统免受对其网络和物理层的威胁。一些作者已经使用例如物理证明来处理重放和完整性攻击，以验证网络过程并检测攻击，或基于水印的检测器，它们也使用物理参数来确保网络层。我们重新检查了基于水印的固定检测器的有效性。我们表明，这种方法仅检测到不试图获取有关系统动力学知识的对手。我们分析了在存在新对手的情况下原始设计的检测比率，这些对手能够推断系统动力学并能够以较高的频率规避检测器。我们提出了一种新的检测方案，该方案采用了几种非平稳水印。我们通过数值模拟和在实验室测试台上运行实验来验证新策略的检测效率。结果表明，所提出的策略能够使用非参数方法来检测对手，