1. Department of Mathematics, Xidian University, China
2. APSIA group, SnT, University of Luxembourg, Coudenhove-Kalergi, Luxembourg
3. School of Computer Science, Guangzhou University, China
4. State Key Laboratory of Integrated Service Networks, Xidian University, China + Network and Data Security Key Laboratory of Sichuan Province, China
5. School of Computer Science and Technology, Xidian University, China
6. State Key Laboratory of Integrated Service Networks, Xidian University, China