  In this paper, we present the synthesis of secure-by-construction controllers
that address safety and security properties simultaneously in cyber-physical
systems. Our focus is on studying a specific security property called opacity,
which characterizes the system's ability to maintain plausible deniability of
its secret behavior in the presence of an intruder. These controllers are
synthesized based on a concept of so-called (augmented) control barrier
functions, which we introduce and discuss in detail. We propose conditions that
facilitate the construction of the desired (augmented) control barrier
functions and their corresponding secure-by-construction controllers. To
compute these functions, we propose an iterative scheme that leverages
iterative sum-of-square programming techniques. This approach enables efficient
computation of these functions, particularly for polynomial systems. Moreover,
we demonstrate the flexibility of our approach by incorporating user-defined
cost functions into the construction of secure-by-construction controllers.
Finally, we validate the effectiveness of our results through two case studies,
illustrating the practical applicability and benefits of our proposed approach.
