Cyber-Physical Systems Security—A Survey <s> VII. CYBER-PHYSICAL SECURITY FRAMEWORK <s> Enter the nascent era of Internet of Things (IoT) and wearable devices, where small embedded devices loaded with sensors collect information from its surroundings, process it, and relay it to remote locations for further analysis. Albeit looking harmless, these nascent technologies raise security and privacy concerns. We pose the question of the possibility and effects of compromising such devices. Concentrating on the design flow of IoT and wearable devices, we discuss some common design practices and their implications on security and privacy. Two representatives from each category, the Google Nest Thermostat and the Nike+ Fuelband, are selected as examples on how current industry practices of security as an afterthought or an add-on affect the resulting device and the potential consequences to the user's security and privacy. We then discuss design flow enhancements, through which security mechanisms can efficiently be added into a device, vastly differing from traditional practices. <s> BIB001 </s> Cyber-Physical Systems Security—A Survey <s> VII. CYBER-PHYSICAL SECURITY FRAMEWORK <s> Cyber-physical systems (CPS) comprise the backbone of national critical infrastructures such as power grids, transportation systems, home automation systems, etc. Because cyber-physical systems are widely used in these applications, the security considerations of these systems should be of very high importance. Compromise of these systems in critical infrastructure will cause catastrophic consequences. In this paper, we will investigate the security vulnerabilities of currently deployed/implemented cyber-physical systems. Our analysis will be from a cross-layer perspective, ranging from full cyber-physical systems to the underlying hardware platforms. In addition, security solutions are introduced to aid the implementation of security countermeasures into cyber-physical systems by manufacturers. Through these solutions, we hope to alter the mindset of considering security as an afterthought in CPS development procedures. <s> BIB002
Now after we have surveyed security in the four CPS applications, we shed light on the relationship between the CPS and security aspects. In Table VI , we summarize the four security issues: 1) threats; 2) vulnerabilities; 3) attacks; and 4) controls with respect to three CPS aspects: 1) cyber; 2) cyber-physical; and 3) physical for ICS, smart grids, medical devices, and smart cars. Please note that the table represents a sample of the surveyed aspects under our framework, and is by no means comprehensive. There are other valuable efforts for CPS security that shed lights on security issues from different angles. For example, Lin et al.  comprehensively surveyed security and privacy, among other issues, in the Internet of Things (IoT). They presented the issues with respect to four layers: 1) perception; 2) network; 3) service; and 4) application. By doing so, they can theoretically dissect the heterogeneous components in IoT for better understanding of the challenges and related issues. They also clarified the relationship between IoT and CPS in a way that distinguishes between the two and demonstrates how they differ. Arias et al. BIB001 explored security and privacy problems in IoT and wearable devices that stem from common practices in the devices' design practices. For example, insecure hardware inevitably will result in insecure software. They show the security and privacy concerns in two devices, the Google Nest Thermostat and the Nike+ Fuelband. Also, they proposed several solutions to address the investigated problems. The solutions include firmware verification, removal/protection of debugging interfaces, the avoidance of using full operating systems in IoT, and use cryptographically signed binaries instead, and securing update channels in wearable devices. In addition, Xu et al.  systematically explored the space of attacks in the some of the smart grids' components from three orthogonal dimensions: 1) attack's target (system operation, communication network, or end user); 2) goal (confidentiality, integrity, or availability); and 3) strength (stealthy or strong) and attacker's system knowledge (full or partial). They also develop a taxonomy of the defenses with three orthogonal dimensions: 1) methodology (reactive and proactive); 2) sources (data and system level); and 3) domains (spatial-and temporal-based). In addition, they propose a framework for investigating the effectiveness of risk analysis, threat detection, and defense reactions in smart grids. The framework applies Markov chains and game theory. Wurm et al. BIB002 investigated CPS security vulnerabilities from a cross-layer perspective (system-, device-, and hardware-level) in several deployed systems, mainly smart home-related devices. They also proposed solutions at every level aiming at improving security considerations in CPS development phases.