1. Computer School, Central China Normal University, 152 Luoyu Road, Wuhan 430079, China
2. Department of Computer Science Electrical Engineering, University of Missouri-Kansas City, 5100 Rockhill Road, Kansas City, MO 64110, USA
3. Department of Computer Science, Wuhan University of Technology, 122 Luoshi Road, Wuhan 430071, China
4. Guangxi Key Laboratory of Trusted Software, Guilin University of Electronic Technology, 1 Jinji Road, Guilin 541004, China