1. School of Computer Science, Nanjing University of Posts and Telecommunications, Nanjing 210003, China. E-mails: lipeng@njupt.edu.cn, 603963049@qq.com, xuhe@njupt.edu.cn
2. Jiangsu High Technology Research Key Laboratory for Wireless Sensor Networks, Nanjing University of Posts and Telecommunications, Nanjing 210003, China. E-mails: lipeng@njupt.edu.cn, xuhe@njupt.edu.cn
3. School of Mathematics and Information Security, Royal Holloway, University of London, Surrey, TW200EX, UK. E-mail: hk.tflau@gmail.com