TITLE: Cyber-Physical Systems under Attack

AUTHORS: Fabio Pasqualetti, Florian Dorfler, and Francesco Bullo
Center for Control, Dynamical Systems and Computation, UC Santa Barbara

WORKSHOP SPEAKERS: Francesco Bullo and Fabio Pasqualetti


ABSTRACT: 

Cyber-physical systems integrate computation, communication, and
physical capabilities to interact with the physical world and
humans. Examples of cyber-physical systems include transportation
networks, power generation and distribution networks, water and gas
distribution networks, and advanced communication systems. Because of
the crucial role of cyber-physical systems in everyday life,
cyber-physical security challenges need to be promptly addressed.

We propose a unified framework to analyze the resilience of cyber-
physical systems against attacks cast by an omniscient adversary. We
model cyber-physical systems as linear descriptor systems, and attacks
as exogenous unknown inputs. Despite its simplicity, our model
captures various real-world cyber-physical systems and it includes and
generalizes the most studied prototypical attacks, including stealth,
(dynamic) false-data injection and replay attacks. For this model, we
study various attack detection and identification procedures, and we
characterize their fundamental limitations. We provide constructive
algebraic conditions to cast undetectable and unidentifiable attacks,
and graph-theoretic conditions for the existence of undetectable and
unidentifiable attacks.

Following our analysis, we propose centralized and decentralized
monitors for attack detection and identification. To be specific, we
first design optimal centralized attack detection and identification
monitors based upon the geometric notion of conditioned invariant
subspace. Optimality refers here to the ability of detecting
(resp. identifying) every detectable (resp. identifiable)
attack. Then, starting from the centralized attack detection monitor
we develop a fully distributed attack detection filter. By means of a
decentralized representation of the system dynamics, we provide a
distributed implementation of the attack detection filter based upon
iterative local computations using the Gauss-Jacobi waveform
relaxation technique. Finally, we show that the attack identification
problem is inherently computationally hard, and we design a
distributed identification method that achieves identification, at a
low computational cost and for a certain class of attacks. Our
distributed identification methods is based upon a divide and conquer
procedure, in which first corrupted regions and then corrupted
components are identified via local identification procedures and
cooperation among neighboring regions.

Finally, we present several illustrative examples that, besides
illustrating our findings, show the effectiveness of our methods also
in the presence of system noise, nonlinearities, and modeling
uncertainties.


BIOSKETCHES

Fabio Pasqualetti is a Doctoral Candidate in Mechanical Engineering at the
University of California, Santa Barbara. He received the Laurea degree
``summa cum laude'' in Computer Engineering from the University of Pisa,
Pisa, Italy, in 2004, and the Laurea Magistrale degree ``summa cum laude''
in Automation Engineering from the University of Pisa, Pisa, Italy, in
2007.  His main research interest is in secure control systems, with
application to multi-agent networks, distributed computing and power
networks. Other interests include vehicle routing and combinatorial
optimization, with application to distributed area patrolling and
persistent surveillance.

Florian Dorfler received his Diplom degree in Engineering Cybernetics from
the University of Stuttgart, Germany, in 2008. He was a visiting student at
the University of Toronto in 2007/2008, a visiting researcher at the
University of California, Santa Barbara in 2009, a corporal research intern
at EADS Astrium in 2008, and graduate research intern at Los Alamos
National Labs in 2011. Since September 2009 he is a Ph.D. candidate in the
Department of Mechanical Engineering at the University of California, Santa
Barbara. His main research interests include distributed systems,
synchronization, and coordinated control with applications in smart power
grids and robotic networks. He is recipient of the 2009 Regents Special
International Fellowship, the 2011 Peter J. Frenkel Foundation Fellowship,
the 2010 ACC Student Best Paper Award, and the 2011 O. Hugo Schuck Best
Paper Award.

Francesco Bullo is currently a Professor with the Mechanical Engineering
Department and the Center for Control, Dynamical Systems and Computation at
the University of California, Santa Barbara.  He was previously associated
with the University of Padova, the California Institute of Technology and
the University of Illinois at Urbana-Champaign. His main research interest
is multi-agent networks with application to robotic coordination,
distributed computing and power networks; he has worked on vehicle routing,
geometric control, and motion planning.  He is the coauthor of "Geometric
Control of Mechanical Systems" (Springer, 2004) and "Distributed Control of
Robotic Networks" (Princeton, 2009).