  Access to the cloud has the potential to provide scalable and cost effective
enhancements of physical devices through the use of advanced computational
processes run on apparently limitless cyber infrastructure. On the other hand,
cyber-physical systems and cloud-controlled devices are subject to numerous
design challenges; among them is that of security. In particular, recent
advances in adversary technology pose Advanced Persistent Threats (APTs) which
may stealthily and completely compromise a cyber system. In this paper, we
design a framework for the security of cloud-based systems that specifies when
a device should trust commands from the cloud which may be compromised. This
interaction can be considered as a game between three players: a cloud
defender/administrator, an attacker, and a device. We use traditional signaling
games to model the interaction between the cloud and the device, and we use the
recently proposed FlipIt game to model the struggle between the defender and
attacker for control of the cloud. Because attacks upon the cloud can occur
without knowledge of the defender, we assume that strategies in both games are
picked according to prior commitment. This framework requires a new equilibrium
concept, which we call Gestalt Equilibrium, a fixed-point that expresses the
interdependence of the signaling and FlipIt games. We present the solution to
this fixed-point problem under certain parameter cases, and illustrate an
example application of cloud control of an unmanned vehicle. Our results
contribute to the growing understanding of cloud-controlled systems.
