关键词: 完美前向安全, 机密性, 协议, 认证性, E-mail

Abstract: In 2005，Sun et al have proposed two secure e-mail protocols with perfect forward secrecy.Although these two protocols seem to be secure from the protective efficiency of the short-term key，yet neither of them has considered the authentication of the delivering ciphertext.If an outside attacker intercepts and modifies a delivering ciphertext，the e-mail receiver will have to accept a false plaintext.To overcome this flaw，in this paper we will make improvements on Sun et al.’s protocols such that the improved protocols have authentication，better security and practicality.

Key words: perfect forward secrecy, confidentiality, protocol, authentication, e-mail