zkSSI: A Zero-Knowledge-Based Self-Sovereign Identity Framework

Self-Sovereign Identity (SSI) empowers holders to control their Verifiable Credentials (VCs) and demonstrate their compliance with verifiers' conditions by sending VCs to the verifiers. State-of-the-art SSI solutions from both industry (e.g., Polygon ID) and academia (e.g., zk-creds) protect holders' privacy by reducing the necessity to transmit these VCs which contain personal data. However, the solutions limit verifiers from expressing and verifying multiple conditions efficiently. This paper introduces zkSSI, which enables verifiers to ex-press complex requirements by combining multiple conditions using logical predicates and nested conditions. zkSSI utilizes zk-SNARKs to generate single or multiple zero-knowledge proofs, validating compliance with verifiers' requirements both on-chain and off-chain. Formal proofs are provided to show the privacy and security guarantees of zkSSI, and experimental results demonstrate its efficiency for both holders and verifiers, even when using consumer-grade hardware.