1. College of Applied Sciences, Beijing University of Technology, Beijing 100124, P. R. China
2. Faculty of Information Technology, Beijing University of Technology, Beijing 100124, P. R. China
3. Beijing Key Laboratory of Trusted Computing, Beijing 100124, P. R. China
4. National Engineering Laboratory for Critical Technologies of Information Security Classified Protection, Beijing 100124, P. R. China
5. Beijing Key Laboratory of Internet Culture and Digital Dissemination Research, Beijing Information Science and Technology University, Beijing 100101, P. R. China