Cryptanalysis of some user identification schemes for distributed computer networks

User identification plays an important role for access control in networks. Recently, Hsu and Chuang proposed a user identification scheme for distributed computer networks, which can also provide key agreement and user anonymity. However, Tsai pointed out the weakness of Hsu-Chuang's scheme and proposed an improved scheme. In this paper, we present two attacks to examine that some user identification schemes have a serious security loophole. Finally, we propose a new user identification scheme, which is more secure than the existing schemes.