Prophecies all the Way: Game-based Model-Checking for HyperQPTL beyond $\forall^*\exists^*$

Abstract

Model-checking HyperLTL, a temporal logic expressing properties of sets of traces with applications to information-flow based security and privacy, has a decidable, but TOWER-complete, model-checking problem. While the classical model-checking algorithm for full HyperLTL is automata-theoretic, more recently, a game-based alternative for the $\forall^*\exists^*$-fragment has been presented. Here, we employ imperfect information-games to extend the game-based approach to full HyperQPTL, which features arbitrary quantifier prefixes and quantification over propositions and can express every $\omega$-regular hyperproperty. As a byproduct of our game-based algorithm, we obtain finite-state implementations of Skolem functions via transducers with lookahead that explain satisfaction or violation of HyperQPTL properties.