Proof-of-work (PoW) cryptocurrencies rely on a balance of security and fairness in order to maintain a sustainable ecosystem of miners and users. Users demand fast and consistent transaction confirmation, and in exchange drive the adoption and valuation of the cryptocurrency. Miners provide the confirmations, however, they primarily seek rewards. In unfair systems, miners can amplify their rewards by consolidating mining power. Centralization however, undermines the security guarantees of the system and might discourage users. In this paper we present Tailstorm, a cryptocurrency that strikes this balance. Tailstorm merges multiple recent protocol improvements addressing security, confirmation latency, and throughput with a novel incentive mechanism improving fairness. We implement a parallel proof-of-work consensus mechanism with $k$ PoWs per block to obtain state-of-the-art consistency guarantees. Inspired by Bobtail and Storm, we structure the individual PoWs in a tree which, by including a list of transactions with each PoW, reduces confirmation latency and improves throughput. Our proposed incentive mechanism discounts rewards based on the depth of this tree. Thereby, it effectively punishes information withholding, the core attack strategy used to reap an unfair share of rewards. We back our claims with a comprehensive analysis. We present a generic system model which allows us to specify Bitcoin, $B_k$, and Tailstorm from a joint set of assumptions. We provide an analytical bound for the fairness of Tailstorm and Bitcoin in honest networks and we confirm the results through simulation. We evaluate the effectiveness of dishonest behaviour through reinforcement learning. Our attack search reproduces known optimal strategies against Bitcoin, uncovers new ones against $B_k$, and confirms that Tailstorm's reward discounting makes it more resilient to incentive layer attacks.

翻译：工作量证明（PoW）加密货币依赖于安全性与公平性的平衡，以维持矿工与用户可持续的生态系统。用户要求快速且一致的交易确认，并以此推动加密货币的采用与估值。矿工负责提供确认，但主要追求奖励。在不公平的系统中，矿工可通过合并算力放大收益，然而中心化会削弱系统的安全保障并可能使用户流失。本文提出Tailstorm——一种实现上述平衡的加密货币。Tailstorm融合了多项近期协议改进，在保障安全性、确认延迟与吞吐量的同时，引入一种提升公平性的新型激励机制。我们实现了每区块包含$k$个PoW的并行工作量证明共识机制，以获得最先进的一致性保证。受Bobtail与Storm启发，我们将各PoW组织成树形结构：通过在每个PoW中嵌入交易列表，降低确认延迟并提升吞吐量。我们提出的激励机制基于该树的深度折减奖励，从而有效惩罚信息隐匿行为——这是攫取超额奖励的核心攻击策略。我们通过全面分析支撑上述主张：提出通用系统模型，基于共同假设集对比特币、$B_k$及Tailstorm进行形式化描述；给出诚实网络中Tailstorm与比特币公平性的解析界，并通过仿真验证结果；通过强化学习评估恶意行为的有效性。我们的攻击搜索复现了针对比特币的已知最优策略，发现了针对$B_k$的新攻击策略，并证实Tailstorm的奖励折减机制使其对激励层攻击具有更强鲁棒性。