[论文解读] An empirical study of availability and reliability properties of the Bitcoin Lightning Network

Finnegan Waugh, Ralph Holz|arXiv (Cornell University)|Jun 25, 2020

Blockchain Technology Applications and Security参考文献 18被引用 8

一句话总结

本文通过在不同交易规模下探测支付路由成功率，并评估节点随时间的存活状态，实证评估了比特币闪电网络的可用性和可靠性。研究发现，仅有约三分之一的接收方能够成功接收支付，主要原因在于通道资金不足和网络信息过时。尽管节点流失率较低，但持续存在的数据过时问题严重影响了网络的可靠性。

ABSTRACT

The Bitcoin Lightning network is a mechanism to enable fast and inexpensive off-chain Bitcoin transactions using peer-to-peer (P2P) channels between nodes that can also be composed into a routing path. Although the resulting possible channel graphs are well-studied, there is no empirical data on the network's reliability in terms of being able to successfully route payments at a given moment in time. In this paper we address this gap and investigate two forms of availability that are a necessary ingredient to achieve such reliability. We first study the Lightning network's ability to route payments of various sizes to nearly every participating node, over most available channels. We establish an inverse relationship between payment volume and success rate and show that at best only about a third of destination nodes can be successfully reached. The routing is hampered by a number of possible errors, both transient and permanent. We then study the availability of nodes in the network longitudinally and determine how long-lived they are. Churn in the network is actually low, and a considerable number of nodes are hosted on cloud providers. By testing node liveness, we find that the propagated network information is relatively often stale, however, both for IP addresses and Tor onion addresses. We provide recommendations how the Lightning network can be improved, including considerations which trade-offs between privacy and decentralization on the one hand and reliability on the other hand should at least be reconsidered by the community developing the Lightning network.

研究动机与目标

• 调查闪电网络中支付路径的实时可用性，填补路由可靠性方面实证数据的空白。
• 测量节点的长期可用性，尤其关注节点存活状态和网络地址过时问题。
• 评估过时信息（尤其是IP地址和Tor洋葱地址）对路由成功率的影响。
• 评估去中心化、隐私与可靠性之间的权衡，特别是公开公网IP地址带来的影响。
• 提出协议与设计改进建议，以提升网络可靠性并减少网络信息的过时现象。

提出的方法

• 对闪电网络进行大规模探测，测试不同支付金额下的支付路由成功率。
• 从多个来源（包括c-lightning客户端）收集并分析网络数据，以评估节点存活状态和地址传播情况。
• 测量网络信息的存活时间（time-to-live），重点关注公网IP地址和Tor洋葱地址。
• 评估c-lightning中现有数据清理机制在清除过时信息方面的有效性。
• 提出一种维护协议，通过模拟支付测试通道和节点可用性，而无需实际资金转移。
• 分析IP地址暴露的威胁模型，认为在法律数据访问限制下，隐私担忧被过度夸大。

实验结果

研究问题

• RQ1 在闪电网络中，向不同目标节点发送各种规模支付的实际成功率是多少？
• RQ2 节点在网络中能保持多长时间的可用性？节点流失率如何？
• RQ3 网络信息（尤其是IP地址和Tor地址）的过时程度有多大？这如何影响路由？
• RQ4 临时性故障（如通道资金不足）和永久性故障（如节点离线）对支付成功率有何影响？
• RQ5 隐藏网络地址对隐私、去中心化和网络可靠性有何影响？

主要发现

• 仅有约三分之一的目标节点能够成功接收支付，且大额交易的成功率显著下降。
• 支付成功率与支付金额呈强烈负相关，仅小额支付有合理的成功机会。
• 通道资金不足导致的临时故障是路由失败的主要原因，同时节点离线等永久性故障也造成显著影响。
• 尽管节点流失率较低，但大量网络信息（包括IP地址和Tor地址）仍处于过时状态，c-lightning的清理机制未能有效消除这些过时数据。
• 隐藏网络地址会损害网络可靠性，且不会显著提升隐私保护，因为托管商或ISP在法律要求下仍可将IP地址与身份关联。
• 作者建议实施一种探测协议，以在不转移资金的情况下测试通道和节点的可用性，从而减少数据过时并提升路由可靠性。