Cyber physical systems are embedded in many aspects of our lives. Challenges securing these systems arise from their constraints and that these systems must interact with both digital and physical entities. Our research develops novel techniques to identify threats and then secure these systems under their constraints such as with limited energy, processing power or memory. This includes operational aspects, but also investigates protecting the information such systems reveal to an adversary in the way they act. We use theoretical analyses as the foundation for our work, which we test in practice to identify and address reality gaps between the theory and practice.