[论文解读] Information Propagation on Permissionless Blockchains.

Oğuzhan Ersoy, Zhijie Ren+2 more|arXiv (Cornell University)|Dec 20, 2017

Blockchain Technology Applications and Security参考文献 29被引用 4

一句话总结

本文通过引入抗女巫攻击的费用分担模型和一种智能路由协议，提出了一种无需许可区块链中的激励相容且带宽高效的资讯传播机制，从而减少冗余通信。它证明了在1-连通网络中无法实现抗女巫攻击性，但表明传播决策可与接收方能力解耦，通过感知最短路径的路由实现最优带宽扩展。

ABSTRACT

Blockchain technology, as a decentralized and non-hierarchical platform, has the potential to replace centralized systems. Yet, there are several challenges inherent in the blockchain structure. One of the deficiencies of the existing blockchains is a convenient information propagation technique enhancing incentive-compatibility and bandwidth efficiency. The transition from a centralized system into distributed one brings along game theoretical concerns. Especially for the permissionless blockchains, information propagation should be incentive-compatible just like any other communication or computational costly operation. Another important issue is that information is relayed via gossip-like protocols causing excessive bandwidth usage. Each information is propagated at least twice: first to advertise its existence, second to announce that it is final and validated, i.e., added to the block. In this work, we investigate two distinct aspects of the information propagation of the blockchains: incentive and routing mechanisms. For the former part, we analyze the necessary and sufficient conditions of the Sybil-proof incentive-compatible propagation methodology. We show the impossibility result of the Sybil-proofness in 1-connected network model. For the rest, we prove that the propagation decision is independent of the capabilities of the receiving side. Then, we formulate the generic fee sharing function which encourages rational participants to propagate information. Regarding the bandwidth efficiency, we study a special type of consensus protocols where the block owner (round leader) is validated before the block is created. We present a smart routing mechanism which the redundant communication cost from the size of the network to the scale of average shortest path length. Finally, we combine the incentive and routing mechanisms in a storage-efficient way.

研究动机与目标

• 解决无需许可区块链中缺乏激励相容且带宽高效的资讯传播问题。
• 分析在去中心化网络中实现抗女巫攻击传播的条件。
• 设计一种通用的费用分摊函数，激励理性节点转发资讯。
• 通过优化路由减少区块链Gossip协议中的冗余通信成本。
• 以存储高效的方式结合激励机制与高效路由。

提出的方法

• 分析1-连通网络模型，证明在资讯传播中无法实现抗女巫攻击性。
• 引入一种通用的费用分摊函数，使节点激励与真实传播保持一致，且独立于接收方能力。
• 提出一种智能路由机制，将冗余通信限制在平均最短路径长度，而非网络规模。
• 设计一种共识协议，确保区块创建前先验证区块所有者，从而实现高效传播。
• 结合激励机制与路由机制，确保经济理性和带宽效率。
• 采用存储高效的设计，将费用分摊与路由无缝集成，不增加额外开销。

实验结果

研究问题

• RQ1 在何种条件下，无需许可区块链中的资讯传播可以实现抗女巫攻击性？
• RQ2 是否可以设计一种激励机制，使传播决策独立于接收方能力？
• RQ3 如何最小化区块链Gossip协议中的冗余通信成本？
• RQ4 能否使路由机制的扩展性基于平均最短路径长度而非网络规模？
• RQ5 如何在区块链资讯传播中同时实现激励相容与带宽效率？

主要发现

• 在1-连通网络模型中，资讯传播的抗女巫攻击性是不可能实现的，确立了根本性限制。
• 传播决策可独立于接收方能力进行，从而实现更可扩展且理性的行为。
• 所提出的通用费用分摊函数确保理性参与者有激励进行真实传播。
• 智能路由机制将冗余通信成本从O(n)降低至O(d)，其中d为平均最短路径长度。
• 联合机制在不增加存储开销的前提下，同时实现了激励相容与带宽效率。
• 协议设计通过将激励与网络拓扑约束解耦，实现了无需许可区块链中高效的信息传播。