HEB: Hybrid Expenditure Blockchain

Abstract

The study of Proof of Work (PoW) has culminated with the introduction of cryptocurrency blockchains like Bitcoin. These protocols require their operators, called miners, to expend computational resources and they reward them with minted cryptocurrency tokens. The system is secure from attackers who cannot expend resources at a rate equivalent to that of all benign miners. But the resource requirement is arbitrary - the product of the number of minted tokens and their real value. We present Hybrid Expenditure Blockchain (HEB), a novel cryptocurrency PoW protocol that allows its designer to tune external expenditure. To the best of our knowledge, this is the first tunable PoW protocol. Despite the reduced resource expenditure, it maintains the security guarantees of pure PoW protocols against rational attacks. HEB has practical implications, as global power expenditure on PoW blockchains exceeds that of a medium-sized country. Applying HEB in operational PoW systems can significantly reduce their ecological footprint.