Cyber-physical systems are a crucial part of modern automation applications. These systems are widespread across the production industry and critical infrastructures where a high degree of security, reliability and availability is required. This work investigates possible defense mechanisms against attacks on cyber-physical systems modeled by networked discrete event systems. Based on a threat assessment, attack prevention, attack detection and localization, and attack recovery methods are proposed. The cyber attacks under consideration are stealthy attacks that actively hide their influence and are not detectable by conventional anomaly detection schemes. The attack prevention is based on a controller encryption scheme exploiting the use of homomorphic encryption. The attack detection and localization are realized by introducing unexpected behavior into the transmitted signals and analyzing the timing behavior. The attack recovery reconfigures the controller based on the information gained from the attack localization and Monte-Carlo Tree Search.weiterlesen