1. Network and Information Center, Institute of Network Technology, Beijing University of Posts and Telecommunications, Beijing 100876, China
2. National Engineering Laboratory for Mobile Network Security (No. [2013] 2685), Beijing University of Posts and Telecommunications, Beijing 100876, China
3. Inspur Electronic Information Industry Co., Ltd, Jinan 250000, China
4. State Key Laboratory of High-end Server and Storage Technology, Jinan 250000, China
5. Ernst and Young, Tokyo, Japan