Digital signature 曹天杰 Tianjie Cao ticao@cumt.edu.cn College of Computer Science and Technology, China University of Mining and Technology, Xuzhou China 中国矿业大学计算机科学与技术学院 2003.6.61 Digital Signature 曹天杰 Tianjie Cao tjcao@cumt.edu.cn College of Computer Science and Technology, China University of Mining and Technology, Xuzhou, China 中国矿业大学计算机科学与技术学院 2003.6.6