1. School of Information Science & Engineering, Lanzhou University, Lan’zhou, China
2. Shaanxi Key Laboratory of Network and System Security and the School of Cyber Engineering, Xidian University, Xi’an, China
3. Division of Mathematical Sciences, Nanyang Technological University, Jurong West, Singapore
4. School of Cyber Engineering, Xidian University, Xi’an, China
5. Key Laboratory of Information Security of Network Systems, College of Computer and Big Data, Fuzhou University, Fuzhou, China