Blockchain empowers a decentralized economy by enabling distributed trust in a peer-to-peer network. Decentralization is a core property of blockchain that not only ensures system security but also enables the democratization of systems and processes through the promise of a distributed peer-to-peer network. However, surprisingly, a widely accepted definition or measurement of decentralization is still lacking. We explore an SoK on blockchain decentralization focusing on measurement, quantification, and methodology. First, we establish a taxonomy for analyzing blockchain decentralization in the five facets of consensus, network, governance, wealth, and transaction by qualitative analysis of existing research. Second, we propose an index that measures and quantifies the decentralization level of blockchain across different facets by transforming Shannon entropy. We verify the explainability of the index via comparative static simulations. We also define and discuss alternative indices, including the Gini Coefficient, Nakamoto Coefficient, and Herfindahl-Hirschman Index (HHI). We provide open-source Python code for calculating the decentralization index by comparing various alternatives on GitHub. Third, by applying our proposed index to empirical research on top DeFi applications, we demonstrate how the three scientific methods of descriptive, predictive, and causal inferences are useful in studying blockchain decentralization. Finally, we identify future research directions: 1) to explore the interactions between different facets of blockchain decentralization, 2) to design blockchain mechanisms that achieve sustainable decentralization, and 3) to study the interplay of decentralization levels and the ends of security, privacy, and efficiency. We also raise challenges in addressing the controversies in blockchain decentralization.

翻译：区块链通过对等网络实现分布式信任，从而赋能去中心化经济。去中心化是区块链的核心属性，不仅保障系统安全，还通过分布式对等网络的承诺推动系统与流程的民主化。然而令人意外的是，目前仍缺乏广泛认可的去中心化定义或度量标准。本文针对区块链去中心化中的度量、量化与方法论展开系统综述。首先，通过定性分析现有研究，我们建立了一个涵盖共识、网络、治理、财富与交易五个维度的区块链去中心化分析分类体系。其次，提出一种基于香农熵变换的指数，用于跨不同维度度量与量化区块链的去中心化水平。通过比较静态仿真验证了该指数的可解释性。我们同时定义并讨论了替代指数，包括基尼系数、中本聪系数和赫芬达尔-赫希曼指数（HHI），并在GitHub上提供用于计算去中心化指数的开源Python代码（含多种替代方案对比）。第三，将该指数应用于顶级DeFi应用的实证研究，展示了描述性、预测性和因果推断三种科学方法在研究区块链去中心化中的有效性。最后，提出未来研究方向：1）探索区块链去中心化各维度间的相互作用，2）设计实现可持续去中心化的区块链机制，3）研究去中心化水平与安全性、隐私性、效率性目标之间的关联。同时指出解决区块链去中心化争议所面临的挑战。