Several blockchain consensus protocols proposed to use of Directed Acyclic Graphs (DAGs) to solve the limited processing throughput of traditional single-chain Proof-of-Work (PoW) blockchains. Many such protocols utilize a random transaction selection (RTS) strategy (e.g., PHANTOM, GHOSTDAG, SPECTRE, Inclusive, and Prism) to avoid transaction duplicates across parallel blocks in DAG and thus maximize the network throughput. However, previous research has not rigorously examined incentive-oriented greedy behaviors when transaction selection deviates from the protocol. In this work, we first perform a generic game-theoretic analysis abstracting several DAG-based blockchain protocols that use the RTS strategy, and we prove that such a strategy does not constitute a Nash equilibrium, which is contradictory to the proof in the Inclusive paper. Next, we develop a blockchain simulator that extends existing open-source tools to support multiple chains and explore incentive-based deviations from the protocol. We perform simulations with ten miners to confirm our conclusion from the game-theoretic analysis. The simulations confirm that greedy actors who do not follow the RTS strategy can profit more than honest miners and harm the processing throughput of the protocol because duplicate transactions are included in more than one block of different chains. We show that this effect is indirectly proportional to the network propagation delay. Finally, we show that greedy miners are incentivized to form a shared mining pool to increase their profits. This undermines the decentralization and degrades the design of the protocols in question. To further support our claims, we execute more complex experiments on a realistic Bitcoin-like network with more than 7000 nodes.

翻译：若干区块链共识协议提出利用有向无环图（DAG）来解决传统单链工作量证明（PoW）区块链处理吞吐量有限的问题。许多此类协议采用随机交易选择（RTS）策略（例如PHANTOM、GHOSTDAG、SPECTRE、Inclusive和Prism），以避免DAG中并行区块间的交易重复，从而最大化网络吞吐量。然而，已有研究未严格审视当交易选择偏离协议时，受激励导向的贪婪行为。本文首先对采用RTS策略的多类DAG区块链协议进行通用博弈论分析，证明该策略不构成纳什均衡，这与Inclusive论文中的证明结论相悖。随后，我们开发了一款扩展现有开源工具以支持多链的区块链模拟器，用于探索基于激励的协议偏离行为。我们通过十名矿工的模拟实验验证了博弈论分析结论：未遵循RTS策略的贪婪参与者可获得高于诚实矿工的收益，并因重复交易被包含在不同链的多个区块中而损害协议处理吞吐量。研究显示，该效应与网络传播延迟呈反比关系。最后，我们证明贪婪矿工有动力组建共享矿池以增加收益，这破坏了相关协议的去中心化特性并降低其设计质量。为支撑结论，我们在含7000多个节点的类比特币网络上执行了更复杂的实验。