  In this study, the authors consider the problem of exchanging secrete
messages in cyber-physical systems (CPSs) without resorting to cryptographic
solutions. In particular, they consider a CPS where the networked controller
wants to send a secrete message to the plant. They show that such a problem can
be solved by exploiting a Wyner wiretap-like encoding scheme taking advantage
of the closed-loop operations typical of feedback control systems.
Specifically, by resorting to the control concept of one-step reachable sets,
they first show that a wiretap-like encoding scheme exists whenever there is an
asymmetry in the plant model knowledge available to control system (the
defender) and to the eavesdropper. The effectiveness of the proposed scheme is
confirmed by means of a numerical example. Finally, they conclude the study by
presenting open design challenges that can be addressed by the research
community to improve, in different directions, the secrete message exchange
problem in CPSs
