1. School of Computer Science and Engineering, Nanyang Technological University, Singapore
2. College of Computer Science and Electronic Engineering, Hunan University, Changsha, Hunan, China
3. Department of Computer Science, City University of Hong Kong, Hong Kong
4. Key Laboratory of Aerospace Information Security and Trusted Computing, Ministry of Education, School of Cyber Science and Engineering, Wuhan University, Wuhan, Hubei, China