Cryptanalysis of Efficient Dynamic ID Based Remote User Authentication Scheme in Multi-Server Environment Using Smart Card

Recently, Amin proposed an efficient dynamic ID-based remote user password authentication scheme for multi-server environment. They claimed that his scheme resisted different possible attacks include off-line identity guessing attack, off-line password guessing attack, and smart card stolen attack. However, we find some weaknesses of his scheme in this article. We show that his scheme is vulnerable to off-line identity guessing with smart card stolen attack and off-line password guessing with smart card stolen attack.