On the Privacy of Khan et al.'s Dynamic ID-Based Remote Authentication Scheme with User Anonymity

Very recently, Khan, Kim, and Alghathbar [6] proposed a dynamic ID-based remote user authentication scheme and claimed that their scheme can provide user anonymity. However, in this article, the authors demonstrate that either a malicious user or an adversary with a valid smart card can trace any user by eavesdropping on his normal authentication session over the public channel. Therefore, Khan et al.'s scheme fails to provide the privacy service as claimed. Hence, the authors present an improved scheme to overcome its flaw and examine the privacy of the improved scheme by using the smart card-based privacy model. In addition, the security and efficiency of the improved scheme are scrutinized. The conclusive result is that the design of the improved scheme is reasonable in not only both privacy and security aspects but also the performance aspect.