zkPoC: A Zero-Knowledge Proof-of-Credit Protocol for Decentralized Lending

Decentralized Finance lending protocols rely on inefficient over-collateralization to mitigate loss risk, as they cannot prevent borrowers from evading on-chain negative history through address switching nor incorporate off-chain credit data without compromising pseudonymity. We propose zkPoC, a zero-knowledge proof-of-credit protocol that addresses both limitations. zkPoC enables borrowers to prove hybrid credit capacity based on combined off-chain credit reports and persistent on-chain credit history, without revealing sensitive credit data, real-world identity, or any observable linkage between an on-chain address and that identity. The protocol introduces a hidden identifier, derived from the borrower's persistent official identity and a secret, that binds every on-chain lending action to one persistent credit history and enables the borrower to prove in zero knowledge that the current off-chain credit report belongs to the same person as that history. This is enforced through zk-SNARKs, nullifiers over counter-chained commitments, and a one-time secret registration through an independent registry, ensuring the three essential security properties of unforgeability, non-reusability, and unlinkability. These properties are formally defined and proven under standard cryptographic assumptions, and jointly satisfy four protocol requirements derived from the core problems. A Circom prototype of the six on-chain circuits measures 10,483–39,454 R1CS constraints and 228,363–352,527 gas per on-chain verification, confirming practical deployability on EVM-compatible chains.