  Cyber-physical systems integrate computation, communication, and physical
capabilities to interact with the physical world and humans. Besides failures
of components, cyber-physical systems are prone to malicious attacks so that
specific analysis tools and monitoring mechanisms need to be developed to
enforce system security and reliability. This paper builds upon the results
presented in our companion paper [1] and proposes centralized and distributed
monitors for attack detection and identification. First, we design optimal
centralized attack detection and identification monitors. Optimality refers to
the ability of detecting (respectively identifying) every detectable
(respectively identifiable) attack. Second, we design an optimal distributed
attack detection filter based upon a waveform relaxation technique. Third, we
show that the attack identification problem is computationally hard, and we
design a sub-optimal distributed attack identification procedure with
performance guarantees. Finally, we illustrate the robustness of our monitors
to system noise and unmodeled dynamics through a simulation study.
