  This paper considers the design of encrypted control systems to secure data
privacy when the control systems operate over a network. In particular, we
propose to combine Paillier cryptosystem with a quantizer whose sensitivity
changes with the evolution of the system. This allows the encrypted control
system to balance between the cipher strength and processing time. Such an
ability is essential for control systems that are expected to run real-time. It
also allows the closed-loop system to achieve the asymptotic stability for
linear systems. Extensions to event-triggered control and nonlinear control
systems are also discussed.
