Advances in Safety and Security of Cyber-Physical Systems: Sliding Mode Observers, Coalitional Control and Homomorphic Encryption

T. Keijzer

Research output: ThesisDissertation (TU Delft)

175 Downloads (Pure)


Without us realizing it, solutions for safety and security are present all around us. However, everyone has undoubtedly also experienced how inconvenient some safety and security measures can be. For example, think about security checks at the airport, the need to wear a bicycle helmet, or being asked to perform 2-factor authentication to log into an online account. Such inconveniences caused by safety and security measures can delay or even prevent their implementation, which is undesired. This reluctance to tolerate inconveniences for the sake of safety and security provides a challenge for engineers to find solutions with minimal impact on normal behaviour.

This challenge is especially pronounced in so-called cyber-physical systems (CPSs), in which digital automation is used to coordinate the actions of one or more physical systems. Examples of CPSs are airplanes, robotic arms or the power grid. Such CPSs have the combined advantages of the physical and cyber world, but are also subject to both threats to safety and security. In fact, the integration of physical and cyber parts in a CPS means that security issues can cause safety issues, and although less common safety issues can cause security issues.

Measures for safety and security of CPSs are categorized as prevention, resilience, and detection & accommodation. These different types of precautions can be used independently, but typically they need to be combined to provide adequate safety and security of a CPS. In this dissertation, three advances within safety and security of CPSs are presented which cover contributions on each of the different types of safety and security measures. Firstly, anomaly detection is addressed by extending existing sliding mode observer (SMO) based anomaly estimation methods with detection capability. To this end, two SMO based anomaly detectors are presented, which are applicable to a large class of SMOs. These detectors, by design, have no false alarms and allow for strong theoretical guarantees on detectability.

Secondly, a topology-switching coalitional control technique which integrates resilience, detection and accommodation is designed for safe control of a collaborative vehicle platoon (CVP) subjected to man-in-the-middle (MITM) cyber-attacks. Here resilience to undetected attacks is achieved by means of scenario-based model predictive control (MPC) and detected anomalies are accommodated by disabling the affected communication links. Lastly, a real-time implementation of encrypted control based on fully homomorphic encryption (FHE) is presented. FHE allows for manipulation of encrypted data, such that it can prevent confidentiality breaches during communication and computation.

Each contribution of this dissertation addresses a specific topic within safety and security of CPSs. By doing so, they demonstrate the potential of these methods to increase safety and security of CPSs while minimizing their impact on normal behaviour. This will promote the adaptation of safety and security measures and allows for safety and security throughout the continued progress in automation.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Delft University of Technology
  • van Wingerden, J.W., Supervisor
  • Ferrari, R., Advisor
Award date13 Feb 2023
Print ISBNs978-94-6384-411-6
Publication statusPublished - 2023


  • Safety & Security
  • Sliding Mode Observer
  • Coalitional Control
  • Homomorphic Encryption
  • Collaborative Vehicle Platoon


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