MAP the Blockchain World: A Trustless and Scalable Blockchain Interoperability Protocol for Cross-chain Applications

Blockchain interoperability protocols enable cross-chain asset transfers or data retrievals between isolated chains, which are considered as one of the core infrastructure for Web 3.0. However, existing protocols either face severe scalability issues due to high on-chain and off-chain cost, or suffer from trust concerns because of centralized architecture. In this paper, we propose MAP, a trustless blockchain interoperability protocol that relays cross-chain transactions across heterogeneous chains with high scalability. First, within MAP, we develop a novel cross-chain relay architecture, which integrates a unified relay chain and on-chain light clients of source chains, allowing the trustworthy retrieval and verification of heterogeneous cross-chain transactions. Furthermore, we reduce cross-chain verification cost by incorporating an optimized on-chain light client scheme that adaptively decouples signature verification overheads from inefficient smart contract execution and offloads them to off-chain provers. For experiments, we conduct the first large-scale evaluation on existing blockchain interoperability protocols. With MAP, the required number of on-chain light clients is reduced from O(N ²) to O(N), with decreasing on-chain cost 35% and 25% off-chain cost when verifying cross-chain transactions. To demonstrate the effectiveness, we deployed MAP in the real world. By 2025, we have supported over six popular public chains, 50 cross-chain applications and relayed over 200K cross-chain transactions worth over 640 million USD. Based on the deployment records, we construct the first real-world cross-chain dataset to further advance blockchain interoperability research.