Cyber-physical systems (CPSs) operate nearly all of society's critical infrastructures (e.g., energy, transportation and medicine). In performing mission critical functions, CPSs exhibit hybrid (both discrete and continuous) behavior as they use digital technology to control and monitor physical processes. CPS security analysis is particularly challenging because an attacker can make use of a wide variety of vulnerabilities in the digital elements of the system (e.g., the network), the physical elements of the system, or some combination.