1. School of Cyber Engineering, Xidian University, Xi'an, China
2. State Key Laboratory of Integrated Services Networks, and the School of Cyber Engineering, Xidian University, Xi'an, Shaanxi, China
3. College of Cyber Security, Jinan University, Guangzhou, China
4. School of Mathematics and Computer Science, Fujian Normal University, Fuzhou, China
5. Department of Computer Science and Engineering, University of Electronic Science and Technology of China, Chengdu, China
6. Department of Information Systems and Cyber Security, The University of Texas at San Antonio, San Antonio, TX, USA
7. School of Information Systems, Singapore Management University, Singapore