  The security in information-flow has become a major concern for
cyber-physical systems (CPSs). In this work, we focus on the analysis of an
information-flow security property, called opacity. Opacity characterizes the
plausible deniability of a system's secret in the presence of a malicious
outside intruder. We propose a methodology of checking a notion of opacity,
called approximate initial-state opacity, for networks of discrete-time
switched systems. Our framework relies on compositional constructions of finite
abstractions for networks of switched systems and their so-called approximate
initial-state opacity-preserving simulation functions (InitSOPSFs). Those
functions characterize how close concrete networks and their finite
abstractions are in terms of the satisfaction of approximate initial-state
opacity. We show that such InitSOPSFs can be obtained compositionally by
assuming some small-gain type conditions and composing so-called local
InitSOPSFs constructed for each subsystem separately. Additionally, assuming
certain stability property of switched systems, we also provide a technique on
constructing their finite abstractions together with the corresponding local
InitSOPSFs. Finally, we illustrate the effectiveness of our results through an
example.
