A remote user authentication scheme using hash functions

Recently, Peyravian and Zunic proposed a simple but efficient password authentication system. Their scheme is based on the collision-resistant hash function, such as SHA-1. Their scheme did not use any cryptosystems (such as DES, RSA, etc.). However, their scheme is vulnerable to guess attack. An attacker can easily obtain a user's password by guessing attack and then impersonate the user to login and access resources in the server. To overcome the vulnerability of their scheme, we propose an improved scheme to enhance security of their scheme in this article.