On Security of Privacy-Preserving Remote User Authentication with K-Times Untraceability

As an important access control technique, k-times anonymous authentication (k-TAA) plays a vital role in ecoupon and e-bill. It allows a user to anonymously authenticate himself to a remote server a bounded number of times. However, most of the existing k-TAA schemes require heavy computation, which brings a challenge to resource-limited devices. In 2018, Tian et al. proposed a privacy-preserving remote user authentication with k-times untraceability. Unlike the traditional k-TAA schemes, Tian et al.'s is more suitable for mobile devices due to avoiding expensive pairing operations. And they claim that their scheme provides user authenticity and k-times untraceability. Unfortunately, in this paper, we find that their scheme is insecure by analyzing it. Their scheme can neither prevent a malicious user from passing the authentication nor trace the identity of a dishonest user authenticating for more than k times. Finally, the corresponding attacks are given. © 2021. All Rights Reserved