关键词: 非否认性, 公平性, 密钥保密性, 鲁棒性, 加密Hash函数

Abstract: In response to the flaws of the CMP1 protocol，this paper proposes an improved protocol which adopts a cryptographic primitive-cryptographic Hash function to protect the confidentiality of e-mail message.This proposed protocol uses FTP method to transmit the non-repudiation evidences of origin and receipt，which not only ensures achievement of fairness，but also further enhances the robustness of the protocol.This proposed protocol is verified to satisfy accountability and fairness by utilizing the extended Qing-logic.

Key words: non-repudiation, fairness, secrecy of key, robustness, cryptographic Hash function