REAFFIRM: Model-Based Repair of Hybrid Systems for Improving Resiliency

Model-based design offers a promising approach for assisting developers to build reliable and secure cyber-physical systems in a systematic manner. In this methodology, a designer first constructs a model, with mathematically precise semantics, of the system under design, and performs extensive analysis with respect to correctness requirements before generating the implementation from the model. However, as new vulnerabilities are discovered, requirements evolve aimed at ensuring resiliency. There is currently a shortage of an inexpensive, automated software that can effectively repair the initial design, and a model-based system developer regularly needs to redesign and reimplement the system from scratch. In this paper, we propose a new methodology along with a MATLAB software called REAFFIRM to facilitate the model-based repair for improving the resiliency of cyber-physical systems. REAFFIRM takes as inputs 1) an original hybrid system modeled as a Simulink/Stateflow diagram, 2) a given resiliency pattern specified as a model transformation script, and 3) a safety requirement expressed as a Signal Temporal Logic formula, and outputs a repaired model which satisfies the requirement. The tool consists of two main modules, model transformation followed by model synthesis. While the latter component is built on top of the falsification tool Breach, to implement the former, we introduce a new model transformation language for hybrid systems, which we call HATL, to allow a designer to specify resiliency patterns. To evaluate the proposed approach, we use REAFFIRM to automatically synthesize the repaired models of four different case studies.