A key component in the security of cyberphysical systems is the ability to detect malicious attacks on their control mechanisms. In this talk, we consider malicious attacks on actuators and sensors of feedback control systems which can be modeled as additive, possibly unbounded, disturbances at the digital (cyber) part of the feedback loop. We precisely characterize the role of the unstable poles and zeros of the system in the ability to detect stealthy attacks in the context of the sampled data implementation of the controller in feedback with the continuous (physical) plant. It is shown that this standard implementation can create additional vulnerabilities to stealthy attacks, and therefore, when security is at stake, it is of paramount importance to have methods to eliminate these vulnerabilities.
Our approach is to consider a dual rate sampled data controller whereby the output is sampled appropriately faster than the zero order hold rate that operates on the control input. With this multirate scheme in place, we can guarantee that stealthy attacks are not possible. Further, we can provide precise trade-offs on performance and safety cost. Examples pertaining to power and reservoir systems are presented. We also conclude with some general rate conditions for security in distributed and networked cyberphysical settings.
Professor Petros G. Voulgaris received the Diploma in Mechanical Engineering from the National Technical University, Athens, Greece, in 1986, and the S.M. and Ph.D. degrees in Aeronautics and Astronautics from the Massachusetts Institute of Technology in 1988 and 1991, respectively. Since 1991, he has been with the Department of Aerospace Engineering, University of Illinois where he is currently a Professor (also appointments with the Coordinated Science Laboratory, and the department of Electrical and Computer Engineering.) His research interests include optimal, robust and distributed control and estimation; networked control; applications of advanced control methods to engineering practice including, power systems, air-vehicle, nano-scale, robotic, and structural control systems. Dr. Voulgaris is a recipient of several awards including the NSF Research Initiation Award, the ONR Young Investigator Award and the UIUC Xerox Award for research. He is also a Fellow of IEEE.