1. Key Laboratory of Aerospace Information Security and Trusted Computing, Ministry of Education, School of Cyber Science and Engineering, Wuhan University, Wuhan, China
2. School of Computer Science and Engineering, Nanyang Technological University, Jurong West, Singapore
3. School of Electronic Information, Wuhan University, Wuhan, China
4. School of Science and Technology, Nottingham Trent University, Nottingham, U.K.