# A Survey on Recent Advanced Research of CPS Security
## 1 Introduction  
Cyber-physical systems (CPSs) integrate sensing, computation, control, and networking into physical objects and infrastructure to connect them to the Internet and to each other. The reductions in hardware and computing costs make it possible to connect more embedded devices to the network and share their data. Thus, recent years have witnessed increasing developments in CPS technologies. Various application scenarios, such as power grids, secure water treatment, the Internet of Vehicles (IoV), health care, and smart homes, are implemented with CPS techniques. These technologies have brought great convenience to production and life. However, these systems are also related to personal privacy and even security. Therefore, they are expected to be robust against different existing and unknown attacks; however, these systems face many challenges with respect to attacks. First, the complexity of CPS components, objects, and communication systems creates great challenges for the security of CPSs. Different sensors, actuators, and control systems need to cooperate and require valid authentication and attestation. Various participants make different operation requests to the controller for distinctive scenarios. Apart from traditional communication methods, more approaches (e.g., vibration, light, and electromagnetism) are utilized to transfer information between different devices. Therefore, any minor miss can lead to severe information leakage or overprivileged permissions. A better understanding of CPS security in a unified framework can offer an overall view for researchers. Accordingly, we can pinpoint the weakness of CPS and propose effective defense schemes against such attacks. Another notable issue is the constrained resources of embedded devices, including memory, computation, and power. Many devices in CPS are deployed in physically inaccessible places and lack follow-up maintenance. Hence, these resource-limited devices cannot afford computing-intensive tasks, which makes their security more challenging. Inmost embedded devices, common security mitigation is not supported. Therefore, we need lightweight cryptography methods, authentication protocols, and intrusion detection to reduce the computational costs and extend their service life. A typical example is wearable devices, which gather people's sports, health, and other routine data [1]. However, due to the restricted battery and computation capability, many manufacturers and app developers do not focus on security concerns. These privacy issues put users' privacy at risk. The heterogeneity and constraints of CPS modules make security protection challenging. Therefore, a comprehensive survey is required to help us identify weak points and new explorations in CPS. In [2; 3], the authors make a functional analysis of security properties for smart home devices. There are also surveys about intrusion detection systems [4], the Internet of Things in industries [5], and authentication schemes [6]. These surveys provide in-depth studies but do not build a comprehensive CPS security framework. Some surveys [7; 8; 9] propose cross-layer security structures to summarize CPS security. However, these works do not focus on the latest high-quality papers and point out the newest trends and shortages. Compared with previous work, our study focuses on high-level papers and proposes a comprehensive CPS security analysis framework. However, the analysis papers are recommended by CCF and CPS-related papers in journals. Some seminal work may be omitted. In this paper, we surveyed the literature on CPS security under a unified security framework consisting of three orthogonal dimensions, as shown in Figure 1. MADC is the study of measure, attack, defense, or control. To help researchers obtain the latest trend, we studied papers published in level A/B security journals/conferences that were recommended by the CCF.