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.

翻译：工作量证明（PoW）区块链已成为开放环境中稳健且有效的共识机制，促使众多加密货币平台的大规模部署与巨额投资。然而，当前广泛部署的PoW实现均基于求解密码学谜题。面对区块链网络的巨大计算能力以及全球对更可持续IT基础设施的追求，研究者十余年来持续探索用有用计算任务替代密码学谜题这一引人关注的方向。本研究对替代任务类别的先决条件进行了全面分析，揭示了引入"有用性"及向密码学谜题之外的任务类别转移所产生的影响。在提炼出先决条件后，我们运用这些条件对现有文献中的设计方案进行了检验。最后，我们讨论了相关技术，并指出了当前研究中的空白。