作者机构:[1]Department of Mathematics, Putian University, Putian, Fujian 351100, China., [2]State Key Laboratory of Information Security, Institute of Software, Chinese Academy of Sciences,Beijing 100049, China.
相关基金:Supported by the National Natural Science Foundation of China (No. 61170246), the Program for New Century Excellent Talents in Fujian Province University of China (No. JK2010047) and the Open Funds of State Key Laboratory of Information Security (Chinese Academy of Sciences) (No. 01-01-1).Acknowledgement s The authors wish to thank anonymous referees for valuable comments and Dr. LIU Huaning for his valuable suggestions during the preparation of the manuscript.