Chain Relay

Chain relay implementations must efficiently balance security, cost, and latency considerations. The most secure relays implement full consensus verification, validating block headers according to the source chain's complete rule set. For proof-of-work chains like Bitcoin, this includes difficulty adjustment validation and accumulated work verification to handle potential chain reorganizations. Gas efficiency is a critical challenge, particularly when relaying data to expensive execution environments like Ethereum. Optimizations typically include batched header submission, where multiple sequential headers are validated in a single transaction, and incremental verification that only checks the minimal required components of the consensus rules. For scalability, many implementations employ a checkpoint system where only every nth header is fully validated, with intermediate headers verified using lighter-weight rules. Advanced relays implement fraud-proof mechanisms where fully validating every header is unnecessary—instead, economic incentives encourage watchers to submit fraud proofs when invalid headers are proposed. To handle the unique cryptographic primitives of source chains that may not be natively available in the destination environment, relays often implement custom precompiles or optimized libraries. For example, Bitcoin's SHA256 verification on Ethereum requires efficient implementation strategies to make relay operation economically viable. Sophisticated relay systems also implement finality awareness, adjusting required confirmation depths based on economic security models that calculate the cost of attack relative to the value being transferred across chains.