  We study the security of Cyber-Physical Systems (CPS) in the context of the
supervisory control layer. Specifically, we propose a general model of a CPS
attacker in the framework of discrete event systems and investigate the problem
of synthesizing an attack strategy for a given feedback control system. Our
model captures a class of deception attacks, where the attacker has the ability
to hijack a subset of sensor readings and mislead the supervisor, with the goal
of inducing the system into an undesirable state. We utilize a game-like
discrete transition structure, called Insertion-Deletion Attack structure
(IDA), to capture the interaction between the supervisor and the environment
(which includes the system and the attacker). We show how to use IDAs to
synthesize three different types of successful stealthy attacks, i.e., attacks
that avoid detection from the supervisor and cause damage to the system.
