Efficient Bitcoin Meta-Protocol Transaction and Data Discovery Through nLockTime Field Repurposing

TL;DR

The paper addresses the high cost and inefficiency of discovering protocol-relevant data in Bitcoin by repurposing the 4-byte nLockTime field as a fixed-size discovery beacon. It proposes a structured header (Magic, Type, Variant, Sequence) within a past-timestamp range to enable constant-time filtering (O(1)) of transactions for protocol-relevant data, while keeping consensus validity intact. Through a progression of proofs-of-concept, it demonstrates simple shard sequencing, Merkle-root based assets, cryptographic binding across two transactions, and multisig-protected assets, each preserving low on-chain costs and enabling verifiable provenance and ownership history. The comparative analysis shows substantial efficiency gains over existing meta-protocols, with a practical path to reducing indexer workload and centralization risks, provided a lightweight registry to minimize header collisions.

Abstract

We describe the Lockchain Protocol, a lightweight Bitcoin meta-protocol that enables highly efficient transaction discovery at zero marginal block space cost, and data verification without introducing any new on-chain storage mechanism. The protocol repurposes the mandatory 4-byte nLockTime field of every Bitcoin transaction as a compact metadata header. By constraining values to an unused range of past Unix timestamps greater than or equal to 500,000,000, the field can encode a protocol signal, type, variant, and sequence identifier while remaining fully valid under Bitcoin consensus and policy rules. The primary contribution of the protocol is an efficient discovery layer. Indexers can filter candidate transactions by examining a fixed-size header field, independent of transaction payload size, and only then selectively inspect heavier data such as OP RETURN outputs or witness fields. The Lockchain Protocol applies established protocol design patterns to an under-optimised problem domain, namely transaction discovery at scale, and does not claim new cryptographic primitives or storage methods.