Remote password authentication with smart cards

In a previous paper (ibid. vol.138, no.3, p.165-168, 1991) Chang and Wu proposed an efficient method for remote password authentication based on the Chinese remainder theorem (CRT). In this correspondence, the authors show that, in their scheme, anyone who possesses the public information in the network can derive some of the secret keys of the password generation centre. Then, that person can reveal the password from the intercepted authenticating message and impersonate the legal user in a later login. Thus, their scheme is breakable.