  We consider the problem of controller design for linear time-invariant
cyber-physical systems (CPSs) controlled via networks. Specifically, we adopt
the set-up that a controller has already been designed to stabilize the plant.
However, the closed loop system may be subject to actuator and sensor attacks.
We first perform a reachability analysis to see the effect of potential
attacks. To further ensure the safety of the states of the system, we choose a
subset of sensors that can be locally secured and made free of attacks. Using
these limited resources, an extra controller is designed to enhance the safety
of the new closed loop. The safety of the system will be characterized by the
notion of safe sets. Lyapunov based analysis will be used to derive sufficient
conditions that ensure the states always stay in the safe set. The conditions
will then be stated as convex optimization problems which can be solved
efficiently. Lastly, our theoretical results are illustrated through numerical
simulations.
