Cyber-physical Systems (CPS) present special problems for security. This dissertation examines the cyber security problem, the physical security problem, the security problems presented when cyber systems and physical systems are intertwined, and problems presented by the fact that CPS leak information simply by being observed. The issues presented by applying traditional cyber security to CPS are explored and some of the shortcomings of these models are noted. Specific models of a "drive-by-wire'' automobile connected to a road side assistance network, a "Stuxnet type'' attack, the smart grid, and others are presented in detail.;The lack of good tools for CPS security is addressed in part by the introduction of a new model, Multiple Security Domains Nondeducibility over an Event System, or MSDND(ES). The drive-by-wire automobile is studied to show how MSDND(ES) is applied to a system that traditional security models do not describe well.;The issue of human trust in inherently vulnerable CPS with embedded cyber monitors, is also explored. A Stuxnet type attack on a CPS is examined using both MSDND(ES) and Belief, Information acquisition, and Trust (BIT) logic to provide a clear and precise method to discuss issues of trust and belief in monitors and electronic reports. To show these techniques, the electrical smart grid as envisioned by the Future Renewable Electric Energy Delivery and Management Systems Center (FREEDM) project is also modeled.;Areas that may lead to the development of additional tools are presented as possible future work to address the fact: CPS are different and require different models and tools to understand.
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