The Next Generation of Anonymous Credentials and Zero-Knowledge Proofs of Knowledge for Private Digital Identity

Abstract

Digital credential wallets manage identity documents such as government IDs and financial certificates, face the trilemma of privacy, security, and usability. Optimizing for anonymity by using Anonymous Credentials enhances privacy, but introduces challenges. Current benchmarks show verification using zero-knowledge proofs of knowledge taking 50–500ms, far exceeding the <1ms of standard credentials, impeding usability. Additionally, anonymity complicates security: preventing multiple-credential issuance (sybil resistance) or enforcing revocation becomes difficult when both users and objects are essentially secret. These issues are urgent due to the EU’s 2026 mandate for EU-wide credential wallet usage, which will drive widespread adoption of digital credential wallets, while critical use cases, like privately combining credentials from multiple issuers for KYC, emphasize the importance of this work.

This thesis extends existing work and develops new, fast cryptographic primitives for privacy preserving credential wallets. It introduces the fastest anonymous credential scheme with a 3.77ms Show+Verify time for 10 attributes, outperforming prior methods by 10-15%. Three extensions enhance this scheme. 1) formalized Identity Binding property for secure multi-issuer, multi-credential verification, with an implementation verifying 16 credentials from unique issuers in 72ms; 2) new nullifier constructions using Σ-protocols without pairings, improving privacy-preserving sybil resistance by 5x over previous approaches; 3) T-SIRIS, a threshold-issued, sybil-resistant identity system with near-constant Show+Verify times, over 30x faster than comparable systems [RAR+24]. These advancements are validated by an open-source Rust benchmarking library, delivering standardized empirical data across anonymous credential schemes.