基于分片的非许可区块链的博弈分析
A Game-Theoretic Analysis of Shard-Based Permissionless Blockchains
摘要：
交易吞吐量低和可扩展性差是比特币等公共区块链共识协议的重要问题。最近在这个方向上的研究工作提出了基于分片的共识协议，其关键思想是在多个委员会（或分片）之间分割交易，然后并行处理这些分片或交易集。这种由多个委员会对不相交的事务或碎片集合的并行处理显著提高了系统的整体可扩展性和事务吞吐量。然而，一个重要的研究差距是缺乏对委员会内理性处理者在这种基于分片的共识协议中的策略行为的理解。这种理解对于制定适当的激励措施至关重要，这些措施将促进委员会内部的合作，防止搭便车。在本文中，我们解决这个研究差距，通过分析处理器的行为，使用博弈论模型，每个处理器的目标是在最小的成本参与协议的最大化其奖励。我们首先分析了N-player静态博弈模型中分片协议的纳什均衡。我们发现，根据奖励共享的方法，处理器可以通过单方面的行为在一个有缺陷的方式，从而导致在社会困境中潜在地增加他们的回报。为了克服这种社会困境，我们提出了一种新的激励兼容的奖励共享机制，以促进处理器之间的合作。我们的数值结果表明，实现大多数合作处理器（确保区块链网络的健康状态所需的），与其他奖励共享机制相比，建议的激励兼容奖励共享机制更容易实现。
英文摘要：
Low transaction throughput and poor scalability are significant issues in public blockchain consensus protocols such as Bitcoins. Recent research efforts in this direction have proposed shard-based consensus protocols where the key idea is to split the transactions among multiple committees (or shards), which then process these shards or set of transactions in parallel. Such a parallel processing of disjoint sets of transactions or shards by multiple committees significantly improves the overall scalability and transaction throughout of the system. However, one significant research gap is a lack of understanding of the strategic behavior of rational processors within committees in such shard-based consensus protocols. Such an understanding is critical for designing appropriate incentives that will foster cooperation within committees and prevent free-riding. In this paper, we address this research gap by analyzing the behavior of processors using a game-theoretic model, where each processor aims at maximizing its reward at a minimum cost of participating in the protocol. We first analyze the Nash equilibria in an N-player static game model of the sharding protocol. We show that depending on the reward sharing approach employed, processors can potentially increase their payoff by unilaterally behaving in a defective fashion, thus resulting in a social dilemma. In order to overcome this social dilemma, we propose a novel incentive-compatible reward sharing mechanism to promote cooperation among processors. Our numerical results show that achieving a majority of cooperating processors (required to ensure a healthy state of the blockchain network) is easier to achieve with the proposed incentive-compatible reward sharing mechanism than with other reward sharing mechanisms.
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