Preserving the confidentiality of sensitive internal actions is a unique challenge in Cyber-Physical Systems (CPSs) due to the inherent external observability of such systems and the tight coupling between their cyber and physical domains. The far-reaching objective of this work is to develop a science of self-obfuscating systems based on the composition of simple building blocks. A model of Nondeducibility composes the building blocks under information flow security properties. To this end, this paper proposes fundamental theories on external observability for basic regular networks and the concept of “event compensation”.