Paper 2026/1725

Proof-of-Uniqueness: Sybil-Resistant Privacy-Preserving Decentralized Identity through Threshold-OPRF and zk-SNARK Registry

Abstract

Several decentralized applications and blockchains, such as blockchain-based voting systems or Proof-of-Social-Capital, require a strict one-account-per-person policy, yet public identity records often expose sensitive attributes or enable offline attribution. This work presents a Proof-of-Uniqueness blockchain-based registry that composes an issuer-signed verifiable credential, two zero-knowledge proofs, a threshold verifiable oblivious pseudorandom function (vOPRF), and a smart contract. The first proof authorizes a blinded evaluation of an issuer's certified canonical identifier, and the second validates the OPRF transcript and binds the resulting global nullifier to a wallet. The design further binds issuer authorization, credential status, validity bounds, canonical encoding, and replay state. Its person-level guarantee is conditional on a stable injective identifier within a coordinated issuance namespace and a stable, valid OPRF key. Confidentiality holds against public observers and against fewer than the OPRF threshold of nodes, but not against an issuer that actively probes its own identifiers. Our prototype couples Noir and UltraPlonk circuits, three local threshold OPRF nodes, and a Solidity contract. For one fixed-schema credential input, it derives a single wallet-bound deterministic nullifier, verifies a real 2,144-byte proof on-chain, and rejects a repeated nullifier with $O(1)$ lookups. One real enrollment consumes 615k gas, and proof construction takes about 65 seconds on one desktop software thread.