This paper is about an encryption based approach to the secure implementation
of feedback controllers for physical systems. Specifically, Paillier's
homomorphic encryption is used to digitally implement a class of linear dynamic
controllers, which includes the commonplace static gain and PID type feedback
control laws as special cases. The developed implementation is amenable to
Field Programmable Gate Array (FPGA) realization. Experimental results,
including timing analysis and resource usage characteristics for different
encryption key lengths, are presented for the realization of an inverted
pendulum controller; as this is an unstable plant, the control is necessarily
fast
