A new method for updating certificate revocation trees (CRT) is proposed. Efficient revocation of publickey certificates is a current issue in public-key Infrastructure because a traditional certificate revocation list uses a large amount of bandwidth. A certificate revocation tree is a hash tree of revoked certificates and reduces a bandwidth consumption up to O(log(n)). In this paper, an implementation of certificate revocation tree with S-expression is presented and the performance of the system is evaluated in terms of communication and computational costs. To update a CRT, we have two algorithms; (1) random insertion