XPull: A Relay-Based Blockchain Intercommunication Framework Achieving Cross-Chain State Pulling

Cross-chain technology, which enables different blockchains to intercommunicate with one another, is challenging. Many existing cross-chain platforms, such as Polkadot and Cosmos, generally adopt a relay-based scheme: A relaychain (relay blockchain) receives and records the state information from every parachain (parallel blockchain), and publish the information on the platform, by which parachains are able to efficiently acquire the state information from one another. In the condition when parachain is consortium blockchain, the cross-chain platform cannot work properly. On the one hand, whether state information is submitted to relaychain is completely decided by the internal decision of parachain. The timeliness of state information cannot be guaranteed. On the other hand, the transfer of state information will be interrupted due to the failure of parachain or relaychain-parachain connection. In this paper, we propose a relay-based blockchain intercommunication framework, called XPull (cross-pulling). Specifically, to ensure the timeliness of state information, we propose a cross-chain state pulling scheme based on cosigned state pulling agreement. To solve the interruption of state transfer, we propose a random scheduling scheme to resume the transfer, or confirm the failure of parachain. The security analysis and experimental results demonstrate that XPull is secure and efficient.