ZK-InterChain: Privacy-Preserving Protocol for Cross-Chain Interactions Between Consortium and Public Blockchains

The increasing fragmentation of blockchain networks, compounded by recurring vulnerabilities in conventional cross-chain bridges—including censorship, replay attacks, and validator collusion—underscores an urgent need for secure and privacy-preserving interoperability protocols. This paper introduces ZK-InterChain, a protocol designed for unidirectional data transfers from consortium to public blockchains. The system empowers users to prove private or semi-private actions, such as verified purchases, without revealing their identities on the public network. The core of ZK-InterChain's architecture features a dual Zero-Knowledge Proof (ZKP) system. A client-side module facilitates user-generated proofs of private activity, while a validator-side module attests to state updates from the consortium chain using aggregated BLS signatures. Privacy is maintained through cryptographic nullifiers and minimal public inputs, which decouple a user's identity from their public-chain activities. Security analysis confirms the protocol's resilience against key attack vectors. Empirical evaluation demonstrates user-side proof generation in approximately one minute and validator-side state attestation in two minutes, with on-chain verification consuming approximately 220k gas. These performance characteristics establish ZK-InterChain as a viable solution for non-immediate, privacy-sensitive applications, such as decentralized reputation systems, post-event credentialing, and anonymous feedback mechanisms.