Improved Synthesis of Nondeterministic Publicly Known Edit Functions for Opacity Enforcement

In this article, we investigate the synthesis problem of edit functions for opacity enforcement in systems modeled as partially observed finite-state automata. For better plausible deniability for the edit functions, in cases where the intruder may learn/know their existence, a synthesis problem for nondeterministic edit functions under a publicly known setting was introduced in the literature, but not yet fully solved. In light of this, we revisit the publicly known edit mechanism by proposing a sound and complete approach for solving the synthesis problem of nondeterministic publicly known edit functions. For practical applications, the edit function is assumed to have limited erasure and insertion ability. Our approach is based on a new labeled finite-state structure, and results in wider applicability than previously-proposed in the literature.