1. School of Cyber Science and Technology and the Key Laboratory of Cryptologic Technology, Shandong University, Qingdao, China
2. Ministry of Education, School of Cyber Science and Engineering, Key Laboratory of Aerospace Information Security and Trusted Computing, Wuhan University, Wuhan, China
3. Department of Computer Science, North Carolina State University, Raleigh, NC, USA
4. School of Computer Science, Wuhan University, Wuhan, China