Abstract: Multi-party authentication protocols are used to assure the security sessions of the Multi participants involved in the protocols.In this paper，based on the operational semantics of security protocols，3-party authentication protocols BNV is analyzed. The result shows that it has agreement and synchronization flaws.For this flaws，the message structure of the protocol is amended and a message term identified the agent is added into the protocol messages.Then，the improved protocol is analyzed，which indicates that it can guarantee agreement and synchronization.Finally，an n-party protocol is presented based on the improved 3-party authentication protocols BNV，which is used to confirm the real identities of n agents.

Key words: 3-party protocol BNV, operational semantics, synchronization, agreement

摘要： 多个主体之间的安全会话需要有可靠的多方认证协议来保证。基于安全协议的操作语义模型，分析了三方认证协议BNV的安全性，结果表明该协议存在一致性和同步性缺陷。为此，修改了协议的消息结构并添加了标识协议主体身份的消息项。对改进后协议的安全性进行分析，结果表明改进后的协议不存在原协议的缺陷，协议参与主体满足一致性与同步性要求。最后，基于改进后协议，提出了一个n方认证协议的协议原型。

关键词: 三方认证协议BNV, 操作语义, 同步性, 一致性