Cyber physical systems security: Analysis, challenges and solutions
Introduction
Cyber physical systems (CPS) are a combination of closely integrated physical processes, networking and computation. The physical process is monitored and controlled by embedded (cyber) subsystems via networked systems with feedback loops to change their behavior when needed (Asare et al., 2012). These subsystems work independently of each other with the ability to interact with the external environment (Ali et al, 2015, Wang et al, 2010). The physical processes are achieved by several tiny devices with sensing, computing and communication (often wireless) capabilities. These physical devices can be identified with physical attributes orinformation sensing equipment, such as infrared sensors or Radio Frequency Identification (RFID), and can then be connected to a networking system, in most cases the Internet, to send the captured data to the computational subsystem (Zhang et al., 2011).
With the increased focus on data handling capacity, data communications capability and integration of information systems, as well as physical devices, the demand for integrating CPS in different fields is also increasing, resulting in widely gained attention not only from universities and research and development labs but also from industry and government agencies (Lu et al., 2015). Prior to the current form, CPS evolved through different stages: Embedded Systems, Intelligent Embedded Systems and Systems of Systems (Sendler, 2013). The current form of CPS is used in many different areas such as the power, petroleum, water industry, chemical engineering, healthcare, manufacturing, transportation, automotive systems, entertainment, consumer appliances, in addition to many other areas that are directly related to people's daily lives. It was estimated that cyber physical components would account for 40% of an automobile's total value by the end of 2015 (NIST, 2012), and that in 2020, around 25 billion uniquely identified objects will be used (Jing et al., 2014).
CPS have many features, such as enabling individual components to work jointly, producing complex systems (Vegh and Miclea, 2014). In CPS, data can be captured by physical objects or sensor devices, and transferred through networks to the control system with the absence, in some cases, of any human to machine interaction (Bhabad and Scholar, 2015). The physical objects are increasingly equipped with, for example, infrared sensors, barcodes or RFID tags which can be scanned by smart devices (Khan et al., 2012). These devices can be connected to the Internet to send the identified data and location placement to be used for monitoring and managing the physical environment (Zhang et al., 2011). The computational and processing units can also be placed in the cloud, with the resulting decisions issued as actions to the physical objects (Khan et al., 2012). As an example of CPS, Industrial Control Systems (ICS) are isolated by communication protocols and operating systems from the outer systems. For the time being, these kinds of systems are increasingly interrelated through the Internet in improving functionality and automation. The increased connectivity of the cyber and physical world brings significant security challenges to the CPS (Shafi, 2012). As the importance of these systems is in improving functionality, the interconnectivity among CPS subsystems is growing (Peng et al., 2013).
Security concerns ranging from application environment and communication technology should be addressed at the early stages of the design (Gamundani, 2015). Moreover, the inherent characteristics and advantages of using available networks, such as Wireless Sensor Networks (WSN), Next-Generation Networks and the Internet, CPS are increasingly facing new security challenges, such as securing protocols and establishing trust between CPS subsystems (Lu et al., 2013). Many of the computing subsystems in CPS are based on commercial-off-the-shelf (COTS) components. The COTS components provide a significant level of control, lower deployment, and lower operational costs in comparison to the traditional vendor specific proprietary and closed-source systems. However, this exposes CPS to more vulnerabilities and threats (Nourian and Madnick, 2014). As an example, industrial control systems have been considered secure when not connected to the outside world (Nourian and Madnick, 2014), without taking into account insider attacks. Thus, this indicates that the extensive connectivity between cyber and physical components raises the important issue of security.
More attacks are expected as many interactions among different components are connected outside of their area to provide better services, such as Smart Grid networks. For example, in the field of the power industry, a power plant monitoring system was attacked in 2010. Consequently, a 900MW load was lost in under 7 seconds. In the energy sector, the Iran Bushehr Nuclear Power Plant computer system was attacked by “Stuxnet” in the same year, which led to severe disorder in the nuclear facilities' automated operations and a serious deterioration in Iran's nuclear program (Peng et al., 2013). According to a CIA report, power systems in several regions outside the United States have been penetrated by attackers, leading to power outage in multiple cities. In the medical field, implanted human medical devices have been attacked by hackers through their wireless communications (Leavitt, 2010).
In the transportation field, an exception in the management system of Japan's control schedule resulted in five Shinkansen operation management system failures. Consequently, 124 trains were delayed while 15 trains were suspended, affecting the travel of 8.12 million people (Peng et al., 2013). It has been demonstrated that airplanes could be controlled by attackers via accessing built-in Wi-Fi services (Nourian and Madnick, 2014). In 2010, CarShark was invented, a software with the ability to remotely turn off a car's engine and brakes leading to a loss of control to stop the car. This software was also able to monitor communications between electronic units, providing incorrect readings, and inputting false data to perform the attack. Meanwhile, in that same year, other attackers succeeded in creating a new virus to attack the Siemens plant control system (Wang et al., 2010).
These security incidents provide enough evidence that attacks on CPS, in particular on the cyber layer, can lead to a great loss in people's livelihoods. Therefore, CPS security is becoming more important than ever and should be taken into consideration in the early stage of the design process. Moreover, advanced CPS security techniques are needed to increase the protection of these increasingly complex interconnected systems (Jalali, 2009). Most of the efforts in security solutions were based on the available solutions designed specifically for classical Information Technology (IT) systems to develop or create advanced solutions. However, these solutions are not designed for CPS (Konstantinou et al, 2015, Wang et al, 2010). Additionally, most of the research focuses on the performance, stability, robustness and efficiency of physical systems rather than security, which is broadly ignored, usually as a result of constrained factors, such as low processing, communication and adequate storage ability capacities. However, if security is disregarded, CPS will not work in a stable manner (Lu et al., 2014). In response to the real need to apply security methods to protect these interconnections, a tight coupling in the interconnections between physical and cyber controlling components is required. Security issues are not new; however, advances in technology make it necessary to produce new approaches to protect data from hazards (Nourian and Madnick, 2014). Additionally, CPS privacy is another serious issue that should be taken into consideration (Lu et al., 2014) in any proposed security solution.
Several papers in the literature discuss CPS security and focus only on particular issues. For example, the focus in Neuman (2009) is on the physical control of the CPS, and the author offers some suggestions for protecting communication channels, real-time requirements and applications. In Lu et al. (2014), a security framework for CPS is proposed with a comprehensive analysis regarding three aspects of security objectives: security in specific, CPS applications and security approaches. However, it does not consider all aspects of security, such as authenticity which is the most important security objective of CPS. The authors in Alvaro et al. (2009) discuss the important challenges that CPS face and provide an analysis of threats and possible attack consequences, as well as explain the differences between traditional IT security and CPS. Even though this study provides a significant discussion, its focus is on developing adversary models of CPS, especially for protecting control systems.
To this end, this paper presents analysis of security issues in CPS with a brief overview of the system level architecture and its components. The contributions of this paper are:
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A state-of-the-art review, an analysis and comparison of security issues for CPS utilizing three-level architecture based on the respective functions of each layer.
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A comparison between CPS security and traditional IT security focusing on distinguishing characteristics, risk assessment and possible attacks at each layer.
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An analysis of CPS security requirements and challenges, a discussion of possible solutions and areas for future research.
The rest of this paper is organized as follows. Section 2 presents Cyber Physical Systems (CPS), differences with the IoT and architecture models. Distinguishing characteristics of CPS and security issues are presented in Section 3. Section 4 provides an analysis of the security issues at the various layers of CPS architecture. Possible CPS security solutions are presented in Section 5 while a discussion and ideas for future research areas are covered in Section 6. Finally, Section 7 concludes the paper with a summary of the findings.
Section snippets
Cyber-physical systems
As computing devices have become lightweight, portable, and capable of being connected with the real world, CPS components can be interconnected through the Internet with the capability of system monitoring and controlling with proper operation and real-time response. CPS provide a coupled environment that contains interconnectivity of thousands of devices, providing more convenience in management and control.
CPS security
In general, the security in CPS is classified into two areas: information (data) security and control security. Information security involves securing information during data aggregation, processing and large-scale sharing in the network environment, especially open loosely coupled networks. Control security encompasses resolving any control issues in the network environment and mitigating the control system from any attacks on system estimation and control algorithms (Cárdenas et al,, Lu et
CPS security analysis
As CPS combine cyber and physical processes, there is an increase in the number of challenges that CPS should be considered when designing a security mechanism for such systems. Furthermore, the environment is continuously changing, and connected devices can be dynamically joined in different places (Mahmoud et al., 2015), which increases the complexity of the required security protection.
Challenges that could be faced in designing a security mechanism include prevention, detection and
CPS security solutions
The importance and requirement of security are different from one application to another. For example, in Intelligent Transportation and Intelligent Medical, data privacy is most important requirement whereas in Intelligent Urban Management and the Smart Grid, data authenticity is more important. There have been many efforts to produce a secure CPS model. Some security solutions and modeling techniques to address security in CPS are presented in this section. The following two subsections
Discussion and future research areas
As listed in Section 3.2, each layer of the CPS faces the threat of many attacks. Handling each attack singly will not help, but will burden or exhaust system resources. Much work has been accomplished in the field of CPS security; however, applying common classical methods, such as cryptography and steganography, to CPS is not sufficient. Furthermore, such methods were not principally designed for interaction operations for different applications. Any CPS security model should include security
Summary
Since it is a comparatively new area, limited work has been accomplished in the security field of CPS. Prior to developing any security model, there is a real need for appropriate analysis and anticipation ability for adversaries. Additionally, the verification process of any proposed security model must not affect real-time operations in the system. Therefore, performing assessment, authentication and access control processes should take place without disrupting the runtime environment. This
Yosef Ashibani is a PhD student in the Department of Electrical, Computer and Software Engineering at the University of Ontario Institute of Technology. His research interests include cyber-physical systems (CPS), Internet of Things (IoT) and smart home security.
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Yosef Ashibani is a PhD student in the Department of Electrical, Computer and Software Engineering at the University of Ontario Institute of Technology. His research interests include cyber-physical systems (CPS), Internet of Things (IoT) and smart home security.
Qusay H. Mahmoud is a Professor of Software Engineering in the Department of Electrical, Computer and Software Engineering at the University of Ontario Institute of Technology in Canada. He was the Founding Chair of the Department and served as Chair between Jan 2013 and June 2015, and more recently he has served as Associate Dean of the Faculty of Engineering and Applied Science at the same university. His research interests include distributed systems and software security.