1. School of Software, Dalian University of Technology, Dalian, P. R. China
2. Department of Computer Science, City University of Hong Kong, Hong Kong, P. R. China
3. International School of Information Science and Engineering, Dalian University of Technology, Dalian, P. R. China
4. The Hubei Engineering Research Center on Big Data Security, School of Cyber Science and Engineering, Huazhong University of Science and Technology, Wuhan, P. R. China
5. Physical Sciences and Engineering College, Cardiff University, Cardiff, United Kingdom
6. College of Computer Science, Sichuan University, Chengdu, P. R. China