Security Issues of Chen et al.'s Dynamic ID-based Authentication Scheme

Chen et al. proposed in 2012, a dynamic ID-based authentication scheme for Telecare Medical Information Systems. Chen et al. preferred simpler computations unlike previous schemes proposed for TMIS, so they designed a computational complexity-free protocol. But it entails many security concerns. Here we show that an adversary can cheat the lawful participants of the scheme, can compute the agreed upon session-key; which renders the communication between the participants as un-confidential. We further illustrate that in-spite of using dynamic identity during login phase their scheme does not provide user anonymity. We also demonstrate that their design invites password guessing attack, stolen verifier attack and has an incomplete password change phase.