Obfuscator Synthesis for Privacy and Utility

We consider the problem of synthesizing an obfuscation policy that enforces privacy while preserving utility with formal guarantees. Specifically, we consider plants modeled as finite automata with pre-defined secret behaviors. A given plant generates event strings for some useful computation, but meanwhile wants to hide its secret behaviors from any outside observer. We formally capture the privacy and utility specifications using the automaton model of the plant. To enforce both specifications, we propose an obfuscation mechanism where an edit function “edits” the plant’s output in a reactive manner. We develop algorithmic procedures that synthesize a correct-by-construction edit function satisfying both privacy and utility specifications. To address the state explosion problem, we encode the synthesis algorithm symbolically using Binary Decision Diagrams. We present EdiSyn, an implementation of our algorithms, along with experimental results demonstrating its performance on illustrative examples. This is the first work, to our knowledge, to successfully synthesize controllers satisfying both privacy and utility requirements.