1. Department of Computing Science, Umeå University, Umeå, Sweden
2. School of Computer Science and Cyber Engineering, Guangzhou University, Guangzhou, China
3. College of Computer Science and Ele-ctronic Engineering, Hunan University, Changsha, China
4. Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg, Esch-Belval Esch-sur-Alzette, Luxembourg