CrossChannel: Efficient and Scalable Cross-Chain Transactions Through Cross-and-Off-Blockchain Micropayment Channel

The surge in blockchain-based cryptocurrencies has created a pressing need for Cross-Chain Transaction (CCTx) solutions. Existing solutions either lack sufficient security, like centralized exchanges, or suffer from poor efficiency and scalability, such as atomic swaps. Inspired by the success of the Lightning Network in accelerating Bitcoin transactions, we propose CrossChannel that establishes cross-and-off-chain micropayment channels to achieve efficient and scalable CCTx. Specifically, we analyze the challenges of extending one-chain channels to cross-chain scenarios caused by the separation of blockchains. To overcome these challenges, we employ the chain relay mechanism to synchronize channel-related information across blockchains and construct the channel management protocol on this basis, ensuring the same security level as one-chain channels in cross-chain settings. We prototype CrossChannel between two Ethereum testnets, comparing its transaction efficiency and costs with a typical HTLC-swap scheme. Results demonstrate the significant advancements in efficiency and scalability offered by CrossChannel. Even with channels closing after just 20 transactions, CrossChannel exhibits a fivefold capacity increase for handling CCTxs compared to HTLC swaps.