[论文解读] Optimizing Virtual Payment Channel Establishment in the Face of On-Path Adversaries

Lukas Aumayr, Esra Ceylan+5 more|arXiv (Cornell University)|Nov 29, 2020

Advanced Wireless Network Optimization参考文献 4被引用 5

一句话总结

本文提出了一种面向链下加密货币网络中虚拟支付通道的需求感知优化框架，将通道创建建模为整数线性规划（ILP），在满足容量和成本约束的前提下最小化路由费用。其主要贡献是提出了一种系统化方法，可战略性地在高需求交易对之间建立虚拟通道，显著降低费用并提升网络效率。

ABSTRACT

Payment channel networks (PCNs) are among the most promising solutions to the scalability issues in permissionless blockchains, by allowing parties to pay each other off-chain through a path of payment channels (PCs). However, routing transactions comes at a cost which is proportional to the number of intermediaries, since each charges a fee for the routing service. Furthermore, analogous to other networks, malicious intermediaries in the payment path can lead to security and privacy threats. Virtual channels (VCs), i.e., bridges over PC paths, mitigate the above PCN issues, as an intermediary participates only once to set up the VC and is then excluded from every future VC transaction. However, similar to PCs, creating a VC has a cost that must be paid out of the bridged PCs' balance. Currently, we are missing guidelines to where and how many VCs to set up. Ideally, VCs should minimize transaction costs while mitigating security and privacy threats from on-path adversaries. In this work, we address for the first time the VC setup problem, formalizing it as an optimization problem. We present an integer linear program (ILP) to compute the globally optimal VC setup strategy in terms of transaction costs, security, and privacy. We then accompany the computationally heavy ILP with a fast local greedy algorithm. Our model and algorithms can be used with any on-path adversary, given that its strategy can be expressed as a set of corrupted nodes that is estimated by the honest nodes. We conduct an evaluation of the greedy algorithm over a snapshot of the Lightning Network (LN), the largest Bitcoin-based PCN. Our results confirm on real-world data that our greedy strategy minimizes costs while protecting against security and privacy threats of on-path adversaries. These findings may serve the LN community as guidelines for the deployment of VCs.

研究动机与目标

• 为解决现有支付通道网络在可扩展性和成本效率方面的不足，通过基于交易需求的虚拟通道建立优化来实现改进。
• 建模链下网络中虚拟通道创建成本与路由费用节省之间的权衡。
• 开发一种形式化优化框架，以计算最优的虚拟通道部署位置，从而最小化总交易成本。
• 在最大化成本效率的同时，确保容量约束和网络可靠性得以维持。

提出的方法

• 将虚拟支付通道网络（VPCN）形式化为图结构，包含物理通道（E_p）和虚拟通道（E_v），在标准PCN模型基础上引入容量和费用参数。
• 使用中间节点构建间接虚拟通道，将虚拟通道创建建模为递归的多级结构。
• 提出一种整数线性规划（ILP），在成本和容量约束下联合优化虚拟通道创建、容量分配和路由决策。
• 引入约束条件，确保虚拟通道容量不超过其构建过程中所使用底层物理通道容量之和。
• 引入二元变量，强制规定在每个递归层级上，每对源-目的地之间最多存在一条虚拟通道。
• 使用包含路由费用和虚拟通道创建成本的费用函数，目标是最小化所有交易的总费用。

实验结果

研究问题

• RQ1 如何战略性地建立虚拟支付通道，以在需求驱动的支付通道网络中最小化总交易成本？
• RQ2 基于交易需求模式，虚拟通道创建成本与路由费用节省之间的最优权衡是什么？
• RQ3 在递归的多跳拓扑中，如何通过底层物理通道容量来约束虚拟通道容量？
• RQ4 哪些结构约束可确保虚拟通道不会过度占用网络中的可用容量？
• RQ5 如何优化网络拓扑，使高需求交易对能最大程度受益于直接虚拟通道？

主要发现

• 所提出的基于ILP的优化框架能够成功计算出虚拟通道的最优配置，从而最小化总交易成本，包括路由费用和创建成本。
• 在高需求交易对之间建立的虚拟通道可显著降低路由费用，其创建成本可通过时间摊销得以回收。
• 该模型确保虚拟通道容量始终受限于其构建过程中所使用底层物理通道容量之和。
• 通过强制规定在任一递归层级上每对源-目的地之间最多存在一条虚拟通道，框架有效防止了过度分配。
• 优化结果生成的网络拓扑既具备成本效益又可靠，减少了对中间节点的依赖并最小化了费用暴露。