  Hyperproperties are commonly used in computer security to define
information-flow policies and other requirements that reason about the
relationship between multiple computations. In this paper, we study a novel
class of hyperproperties where the individual computation paths are chosen by
the strategic choices of a coalition of agents in a multi-agent system. We
introduce HyperATL*, an extension of computation tree logic with path variables
and strategy quantifiers. HyperATL* can express strategic hyperproperties, such
as that the scheduler in a concurrent system has a strategy to avoid
information leakage. HyperATL* is particularly useful to specify asynchronous
hyperproperties, i.e., hyperproperties where the speed of the execution on the
different computation paths depends on the choices of the scheduler. Unlike
other recent logics for the specification of asynchronous hyperproperties, our
logic is the first to admit decidable model checking for the full logic. We
present a model checking algorithm for HyperATL* based on alternating word
automata and show that our algorithm is asymptotically optimal by providing a
matching lower bound. We have implemented a prototype model checker for a
fragment of HyperATL*, able to check various security properties on small
programs.
