Enforcing Current-State Opacity and Utility of Cyber-Physical Systems Using Multipath Event Routing

Several strategies have been proposed in the literature to ensure data security in cyber-physical systems abstracted as networked discrete-event systems, such as enforcing opacity by using obfuscation policies. In these cases, if it is considered the existence of an intended receiver, the useful information can be hidden from him/her. This problem becomes worse when the confidentiality of the data must be ensured, i.e., when the intended receiver must always know the system current state from the observation of the obfuscated transmitted sequence. In this paper, we propose a defense strategy to enforce current-state opacity using an obfuscation policy based on event replacements that also ensures the utility of the transmitted information. The notion of utility used, called current-state utility, is associated with the ability of the intended receiver to be always certain of the system current state. In order to implement the defense strategy, a multipath event routing technique is considered.