Robust chaotic map-based authentication and key agreement scheme with strong anonymity for telecare medicine information systems.

To ensure only authorized access to medical services, several authentication schemes for telecare medicine information systems (TMIS) have been proposed in the literature. Due to its better performance than traditional cryptography, Hao et al. proposed an authentication scheme for TMIS using chaotic map based cryptography. They claimed that their scheme could resist various attacks, including the smart card stolen attack. However, we identify that their scheme is vulnerable to the stolen smart card attack. The reason causing the stolen smart card attack is that the scheme is designed based on the assumption that the scheme itself achieves user untraceability. Then, we propose a robust authentication and key agreement scheme. Compared with the previous schemes, our scheme not only enjoys more security features, but also has better efficiency. Our analysis indicates that designing a two-factor authentication scheme based on the assumption that privacy protection is achieved in the scheme itself may pose potential security risks. The lesson learned is that, we should avoid this situation in the future design of two-factor authentication schemes.