1. Network and Data Security Key Laboratory of Sichuan Province, School of Information and Software Engineering, University of Electronic Science and Technology of China, Chengdu, China
2. School of Computer Science Engineering, University of Electronic Science and Technology of China, Chengdu, China
3. Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, NE, USA
4. Department of Electrical and Computer Engineering, University of Windsor, Windsor, ON, Canada
5. Department of Electrical and Computer Engineering, University of Waterloo, Waterloo, ON, Canada