中文摘要：

ZHANG En received his M.S. degree in computer application from China University of Geosciences in 2006. He is currently a Ph.D candidate of the College of Computer Science and Technology in 13eijing University of Technology. His current research interestsinclude information security and computer networks. E-maih zhangenzdrj@163.com. CAI Yongquan received his M.S. degree in computer application from Northwest Polytechnic University in 1992 and Ph.D. degree in computer application from Beijing Agriculture Engineering in 1998. He is currently an professor and doctoral supervisor of College of Computer Science and Technology, BeJjing University of ]~chnology. His research interests include inibrrnation security, computer network. cryptographic protocols analysis and formal methods in cryptography.