On Replacing Cryptopuzzles with Useful Computation in Blockchain Proof-of-Work Protocols
Andrea Merlina, Thiago Garrett, Roman Vitenberg
TL;DR
The paper investigates the feasibility of replacing cryptopuzzles in Proof-of-Work blockchains with useful computation. It formalizes a Block Task interface and a taxonomy of Block Task Properties, showing how the Bitcoin backbone's safety and liveness goals depend on cryptopuzzle-specific features. Through a systematic analysis of candidate task classes (notably k-OV, TSP, and DL) and a survey of 36 proposals, the authors demonstrate that usefulness often conflicts with key properties such as randomness, non-amortizability, and decentralization, and that no design presently achieves full equivalence. The work highlights major research gaps, including formalizing task usefulness, developing reliable difficulty control, and designing robust incentives, offering a framework to guide future PoW designs.
Abstract
Proof-of-Work (PoW) blockchains have emerged as a robust and effective consensus mechanism in open environments, leading to widespread deployment with numerous cryptocurrency platforms and substantial investments. However, the commonly deployed PoW implementations are all based on solving cryptographic puzzles. Researchers have been pursuing the compelling idea of replacing cryptopuzzles with useful computing tasks for over a decade, in face of the substantial computational capacity of blockchain networks and the global pursuit of a more sustainable IT infrastructure. In this study, we conduct a comprehensive analysis of the prerequisites for alternative classes of tasks. We provide insight into the effect of introducing "usefulness" and of transitioning to task classes other than cryptopuzzles. Having distilled the prerequisites, we use them to examine proposed designs from existing literature. Finally, we discuss pertinent techniques and present research gaps in the current state-of-the-art.