Abstract: The design of secure and practical key agreement protocol under multi-server is a hot topic in the field of information security.Based on the general principles of protocol design,this paper discussed the research of an anonymous multi-server key authentication protocol scheme based on biological characteristics designed by Wang et al.It pointed out that server counterfeiting attack,smart card loss attack and session key leakage attack can be realized in this protocol.At the same time,due to the failure of user anonymity,it is easy to leak user privacy,so it is not suitable for practical application.To remedy these shortcomings,a key improvement protocol based on RSA was proposed.In the registration stage,RC and server share different keys and time markers,which can effectively resist server counterfeiting attacks and achieve anonymity and untraceable ability.In the login phase,the protocol uses public key technology to rea-lize the login and forward security of users’ dynamic identity.In the authentication stage,the protocol includes three times of mutual authentication,does freshness detection of messages,and realizes mutual authentication to prevent replay attacks and so on.Finally,the security analysis and efficiency analysis of the possible attacks prove that the improved protocol can resist the attacks of losing smart card,anonymity and so on.At the same time,it maintains a simple operation.

Key words: Anonymity, Forward security, Key agreement, Multi-server, RSA