Comparative Evaluation of Threshold-based Anonymous Credential Systems over Blockchain

Abstract

Decentralized applications (DApps) over blockchains often require the user’s personal information for authentication. However, the public and transparent nature of blockchains can compromise user privacy. Threshold-based anonymous credentials (TAC) provide anonymous and unlinkable authentication, which helps preserve user privacy. Additionally, the design of TAC aligns well with blockchain’s decentralized nature because TAC offers decentralized trust distribution to prevent a single point of failure. However, only a few of them have implementations over blockchains because TAC requires computationally expensive cryptographic operations such as pairings and verification of zero-knowledge proofs (ZKPs) to be done on-chain. Thus, existing TAC systems have not been evaluated in a public permission-less blockchain environment. This evaluation is crucial to assess the efficiency and practicality of deploying TAC in real-world blockchain use cases to make TAC based DApps development feasible. This work presents the design and evaluation of three state-of-the-art TAC systems, RP-Coconut, threshold BBS+ (T-BBS+), and BBS (T-BBS), over the Ethereum blockchain. The evaluation compares the performance of these TAC systems on the Sepolia testnet in terms of execution time and gas usage. Additionally, this work also proposes partial credential verification mechanisms for T-BBS+ and T-BBS that significantly reduce the complexity of identifying valid credentials, thereby lowering the execution time at the user’s end. Furthermore, the implementation for blind issuance and associated ZKPs for T-BBS is provided, which was not previously detailed in the literature and is critical for its correct implementation.