Enforcing Security on Autonomous Vehicle Searches Through the Quantification of Opacity

Abstract

Recently, topics of security have been explored in the field of discrete-event systems (DES). By modelling these systems with DES, the evolution of the processes can be captured, allowing for different vulnerabilities to be noticed. The DES field also provides a different set of tools which can generate new strategies to tackle the security problems in these systems. The motivating problem that this work focuses on is a group of autonomous vehicles traversing some terrain while trying to cooperatively complete a task such as searching for a target. This work shows that strategies can be employed that remove the need for communication under certain conditions. When no such strategy can be developed, it can be useful to have a tool to classify a system’s security. In DES, this has traditionally been captured by the notion of opacity. Unfortunately, this framework has many limitations. Opacity can only be applied to systems with a specific secret and it cannot tell you how obscured a system is. To address these failings, this work develops the concept of degree of opacity. This framework can measure the degree to which a system is secure based on a supplied criterion. It also can be applied to systems as a whole eliminating the dependency on a specific secret. Degree of opacity is a more general version of opacity and can be handled in similar ways. Degree of opacity can be enforced using supervisory control to produce a minimally restrictive supervisor. Alternatively, what is communicated to a vehicle or observed by a vehicle can be controlled, rather than restricting the vehicle’s movements. Unfortunately, non-monotonicity of observability means that it cannot be easily used to enforce degree of opacity like controllability was. To combat this, a strategy called transition pairing is developed which allows monotonicity to be achieved. This strategy is applied to construct an algorithm to pick which communications can be communicated to achieve a target degree of opacity.