关键词: 安全协议, Yahalom协议, 协议时序, 时序缺陷, 安全攻击

Abstract: This paper researches the Yahalom protocol and its variants, finds a sequence flaw existing in them and provides a kind of method to attack them by using the flaw. The Yahalom protocol has been revised several times, and no key-compromise problem is proved in the final Yahalom-Paulson protocol, but the Yahalom protocol and its variants still have the sequence flaw which has never been paid attention before. The Yahalom-Paulson protocol is improved from the angle of sequence. The improved Yahalom-Paulson protocol preserves the security of the original protocol, and can resist the attack caused by the sequence flaw.

Key words: security protocol, Yahalom protocol, protocol sequence, sequence flaw, security attack