An improved client-to-client password-based authenticated key agreement scheme

Recently, Chang, Yang, and Hwang presented a client-to-client password-based authenticated key agreement scheme, which contains a protected password change protocol to allow two parties to arbitrarily change their passwords. However, their protected password change protocol is found to be vulnerable to a denial-of-service attack. In addition, we also find that their protected password change protocol is not easily reparable. In this paper, we propose an improved protected password change protocol that can resist the denial-of-service attack and can be repaired easily.