1. Key Laboratory of Computational Science and Application of Hainan Province, Hainan Normal University, Haikou 571158, P. R. China
2. School of Computer, Nanjing University of Posts and Telecommunications, Nanjing 210003, P. R. China
3. State Key Laboratory of Information Security, Beijing 100093, P. R. China
4. Advanced Cryptography and System Security Key, Laboratory of Sichuan Province, Chengdu University of Information Technology, Chengdu 610073, P. R. China
5. Yangzhou High School of Jiangsu Province, Yangzhou 225002, P. R. China