Opacity is a powerful confidentiality property that holds if a system cannot leak secret information through observable behavior. In recent years, time has become an increasingly popular attack vector. The notion of opacity has therefore been extended to timed automata (TA). However, the verification of opacity of TA has been proven to be undecidable for the commonly used dense time model. To make the problem decidable, state of the art approaches consider weaker notions of opacity or heavily restrict the class of considered TA, resulting in unrealistic threat models.

In this paper, we address the problem of verifying opacity of TA without restrictions. For this purpose, we consider a discrete time setting. We present a novel algorithm to transform TA to equivalent finite automata (FA) and then use known methods to verify opacity of the resulting FA. To improve the efficiency of our algorithm, we use a novel time abstraction that significantly reduces the state space of the resulting FA, improving the scalability of our approach. We validate our method using randomized systems, as well as four case studies from the literature showing that our approach is applicable in practice.