Secure and Portable Anonymous Credentials without Tamper-Resistant Hardware
Tianshu Yu, Kunpeng Bai · 2024
Authentication is a key technology that provides trusts in cyberspace. Anonymous credentials are aimed at providing user authentication and protecting users' privacy meanwhile. Existing anonymous credential protocols mostly rely on specific hardware to protect their credential secrets, the inconvenience of which and the fact that losses or damages of the hardware can make their identities unavailable significantly hamper large-scale deployments of these schemes. In this paper, based on Zhang et al.'s password-based credential techniques (NDSS'20), combined with cryptographic primitives such as non-interactive zero knowledge proofs and homomorphic encryption, we propose a secure and portable anonymous credential protocol which does not need tamper-resistant hardware. Our anonymous credentials are designed to be encrypted using passwords which can be implemented and deployed in software only in the user terminal. The structure of our (encrypted) credentials and the design of our verifier-designated authentication tokens ensure the resistance of our protocol against serious offline dictionary attacks. We further balance security and user privacy, and propose a concept of maximum authentication failure time limit combined with hash computation and zero-knowledge proofs against online dictionary attacks, which are more difficult to defend against in the anonymous authentication setting. Our protocol supports not only blind issuance of anonymous credentials but also anonymous authentication of users. From the perspective of the dominating exponentiation computations in anonymous credential protocols, our anonymous authentication protocol outperforms most existing schemes except the ones that do not provide blind issuance.