Dynamic enforcement of abstract separation of duty constraints

Abstract

Separation of Duties (SoD) aims at preventing fraud and errors by distributing tasks and associated authorizations among multiple users. Li and Wang [2008] proposed an algebra (SoDA) for specifying SoD requirements, which is both expressive in the requirements it formalizes and abstract in that it is not bound to a workflow model. In this article, we bridge the gap between the specification of SoD constraints modeled in SoDA and their enforcement in a dynamic, service-oriented enterprise environment. We proceed by generalizing SoDA's semantics to traces, modeling workflow executions that satisfy the respective SoDA terms. We then refine the set of traces induced by a SoDA term to also account for a workflow's control-flow and role-based authorizations. Our formalization, which is based on the process algebra CSP, supports the enforcement of SoD on general workflows and handles changing role assignments during workflow execution, addressing a well-known source of fraud. The resulting CSP model serves as blueprint for a distributed and loosely coupled architecture where SoD enforcement is provisioned as a service. This concept, which we call SoD as a Service, facilitates a separation of concerns between business experts and security professionals. As a result, integration and configuration efforts are minimized and enterprises can quickly adapt to organizational, regulatory, and technological changes. We describe an implementation of SoD as a Service, which combines commercial components such as a workflow engine with newly developed components such as an SoD enforcement monitor. To evaluate our design decisions and to demonstrate the feasibility of our approach, we present a case study of a drug dispensation workflow deployed in a hospital.