Paper 2026/119

Re2creds: Reusable Anonymous Credentials from Malleable NIZK and Legacy Signatures

Abstract

Decentralized identity is revolutionizing secure digital interactions by giving users control over their personal data. Anonymous credentials (ACs) are fundamental to this paradigm, yet their practical application is hindered by significant usability and efficiency challenges. Existing AC systems often struggle with limitations in predicate expressiveness, privacy protection, and incompatibility with widely adopted legacy signatures based on recommended curves. To overcome these obstacles, this paper introduces a novel AC system named Re2creds. Re2creds establishes a new paradigm of reusable credential presentation, which drastically cuts computational costs by allowing the core of a presentation to be reused across multiple sessions with only lightweight updates. Furthermore, Re2creds incorporates a proof combination mechanism that efficiently supports legacy signatures by moving the most computationally intensive cryptographic operations outside the arithmetic circuit. This approach makes it practical to use credentials based on NIST-recommended curves, removing a critical barrier to real-world adoption. We demonstrate Re2creds’ security properties through a refined UC ideal functionality, accompanied by rigorous proofs. Experimental evaluations demonstrate significant performance improvements over existing schemes: credential generation time decreases by more than 50% when derivingfrom an existing presentation. Additionally, Re2creds makes the presentation of legacy signatures feasible compared to other ACs, which takes less than 1s for a BLS signature based on BN254.