Maximum Information Release While Ensuring Opacity in Discrete Event Systems

Opacity is important in investigating secrecy, privacy, and other properties in general systems that can be modeled as discrete event systems. To ensure opacity, a controller may be used to control information released to the public. For transparency and other reasons, it is often desired that the information released to the public be maximum, as long as opacity is not violated. In this paper, we investigate how to release the maximum information while ensuring opacity. We find a necessary and sufficient condition for an information release policy to ensure opacity. We also develop methods and algorithms to design a controller that releases maximum information. We consider both strong opacity and weak opacity. We apply the results to the dining cryptographers problem. Note to Practitioners-Nowadays, networks and computers make the collection, storage and dissemination of information much easier. This brings us a lot of convenience, but at the same time, also brings us the worry that some private information may be released to the public undesirably. The problem of how to control the release of information thus becomes very important. In this paper, we propose a discrete-event-system approach to investigate the information release problem. The solution can ensure the opacity of private information while releasing the maximum information to the public. We believe that the practitioners both in the field of system and control and in the field of information science will benefit from the results.