An improvement on authenticated key agreement scheme

Over the insecure network environment, key agreement is essential for protecting the messages exchanged between two communication parties. And to achieve high security requirements, key agreement schemes providing mutual authentication are commonly used in modern information security systems. In 2005, Lee and Lee proposed a novel authentication with key agreement scheme. But we find that Lee-Lee's scheme is vulnerable to an off-line password guessing attack. In this paper, we describe the weakness of Lee-Lee's scheme and also propose an improved scheme with better security strength.