关键词: 加密, 数字签名, 数字证书, 时间戳, 智能客户端

Abstract: Aiming at the four problems of downloading the contest paper simultaneously，submitting the answer papers simultaneously，validating the identity of players and validating the integrality in the China undergraduate mathematical contest in modeling，a corresponding PKI-based security solution is put forward with the help of comprehensive application of data encryption，digital signature，digital certificate and time-stamp technique to solve a series of security problems such as privacy，integrality，undeniability and cheat-preventing.At the same time，the time efficiency in the process of downloading and submitting test paper are solved with the help of encryption and time-stamp.Finally，concerning the problems of implementation of encryption and digital signature in B/S mode，it develops a smart client program for contest test with paper encryption，digital signature and time-stamp functions.

Key words: encryption, digital signature, digital certificate, time stamp, smart client