Modeling System Security Rules with Time Constraints Using Timed Extended Finite State Machines

Security and reliability are of paramount importance in designing and building real-time systems because any security failure can put the public and the environment at risk. In this paper, we propose a framework to take timed security requirements into account from the design stage of the system building. Our approach consists of two main steps. First, the system behavior is specified based on its functional requirements using TEFSM (Timed Extended Finite State Machine) formalism. Second, this model is augmented by applying a set of dedicated algorithms to integrate timed security properties specified in Nomad language. Nomad is a formal language well adapted to express timed security properties with timed constraints. We also briefly present a France Telecom Travel system as a case study to demonstrate the reliability of our framework.