Quantitative analysis of distributed systems

Computing Science addresses the security of real-life systems by using various security-oriented technologies (e.g., access control solutions and resource allocation strategies). These security technologies significantly increase the operational costs of the organizations in which systems are deployed, due to the highly dynamic, mobile and resource-constrained environments. As a result, the problem of designing user-friendly, secure and high efficiency information systems in such complex environment has become a major challenge for the developers. In this thesis, firstly, new formal models are proposed to analyse the secure information flow in cloud computing systems. Then, the opacity of workflows in cloud computing systems is investigated, a threat model is built for cloud computing systems, and the information leakage in such system is analysed. This study can help cloud service providers and cloud subscribers to analyse the risks they take with the security of their assets and to make security related decision. Secondly, a procedure is established to quantitatively evaluate the costs and benefits of implementing information security technologies. In this study, a formal system model for data resources in a dynamic environment is proposed, which focuses on the location of different classes of data resources as well as the users. Using such a model, the concurrent and probabilistic behaviour of the system can be analysed. Furthermore, efficient solutions are provided for the implementation of information security system based on queueing theory and stochastic Petri nets. This part of research can help information security officers to make well judged information security investment decisions.