Blockchains protect an ecosystem worth more than $500bn with their strong security properties derived from the principle of decentralization. Is today's blockchain really decentralized? In this paper, we empirically studied one of the {\em least decentralized} parts of Ethereum -- the most used blockchain system in practice -- and shed light on the decentralization issue from a new perspective. To avoid centralization caused by Maximal Extractable Value (MEV), Ethereum adopts a novel mechanism that produces blocks through a {\em builder market}. After two years in operation, however, the builder market has evolved to a highly centralized one with three builders producing more than 90% of blocks. {\em Why does the builder market centralize, given that it is permissionless and anyone can join?} Moreover, {\em what are the security implications of a centralized builder market to MEV-Boost auctions?} Through a rigorous empirical study of the builder market's core mechanism, MEV-Boost auctions, we answered these two questions using a large-scale auction dataset we curated since 2022. Unlike previous works that focus on {\em who} wins the auctions, we focus on {\em why} they win, to shed light on the {openness, competitiveness, and efficiency} of MEV-Boost auctions. Our findings also help identify directions for improving the decentralization of builder markets.

翻译：区块链凭借其源于去中心化原则的强安全属性，保护着价值超过5000亿美元的生态系统。然而，当今的区块链是否真正实现了去中心化？本文针对实践中使用最广泛的区块链系统——以太坊中“去中心化程度最低”的环节之一展开实证研究，从一个新视角剖析了去中心化问题。为避免最大可提取价值（MEV）导致的中心化，以太坊采用了一种通过“构建者市场”生成区块的创新机制。然而，经过两年运行，该市场已高度中心化：仅三家构建者便生产了超90%的区块。在无需许可且人人可加入的前提下，为何构建者市场会趋于中心化？此外，中心化的构建者市场对MEV-Boost拍卖存在哪些安全影响？通过系统研究构建者市场的核心机制MEV-Boost拍卖，我们利用自2022年起收集的大规模拍卖数据集解答了上述两个问题。不同于以往聚焦“谁”赢得拍卖的研究，我们关注“为何”他们能获胜，以揭示MEV-Boost拍卖的开放性与竞争力及效率。研究结果亦有助于明确改善构建者市场去中心化程度的方向。