1. State Key Laboratory of Computer Science, Institute of Software, Chinese Academy of Sciences, P.O. Box 8717, Beijing, China
2. College of Information Engineering, Capital Normal University, Beijing, China
3. Computer Science and Communications, Faculty of Science, Technology and Communication, University of Luxembourg, Walferdange, Luxembourg
4. Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg, Walferdange, Luxembourg