Technology: Cross-chain transaction validation

BXHub utilizes a ChainRelay component running in routers to validate the transaction inclusion on connecting blockchains. The ChainRelay provides two functionalities: Block header migration and Transaction inclusion verification.

Block header migration.

The ChainRelay continuously receives the propagation requests of block headers from the nodes or clients of the blockchain. For each given block header, ChainRelay needs to verify it is part of the souring blockchain. The block headers verification depends on the consensus mechanism used by the connecting blockchains. For Nakamoto consensus, the ChainRelay must get the difficulty adjustment policy, and verify each received header that is on the main chain, with the most accumulated Proof-of-Work. For Proof-of-Stake blockchains, the ChainRelay needs to know the epochs of the staking, and verify the threshold/multi-signatures of each received block header is from the elected leaders. For permissioned blockchain (Proof-of-Authority), the ChainRelay needs to verify the signature of the block header is from consensus participants.

Transaction inclusion verification.

The ChainRelay stores block headers information for all connecting blockchains, which is responsible for verifying a transaction is included in one connecting blockchain. The verification mechanism is based SPV technique, where the ChainRelay receives the Merkle tree proof and transaction data for verifying.