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采用工作量证明共识机制的区块链中挖矿攻击者间的“鲶鱼效应”
引用本文:阮娜,刘汉卿,斯雪明.采用工作量证明共识机制的区块链中挖矿攻击者间的“鲶鱼效应”[J].计算机学报,2021,44(1):177-192.
作者姓名:阮娜  刘汉卿  斯雪明
作者单位:上海交通大学电子信息与电气工程学院 上海200240;上海交通大学电子信息与电气工程学院 上海200240;中原工学院前沿信息技术研究院 郑州450007;复旦大学计算机科学技术学院上海市数据科学重点实验室 上海201203
基金项目:本课题得到国家自然科学基金青年基金
摘    要:近年来,采用工作量证明共识机制(Proof of Work,PoW)的区块链被广泛地应用于以比特币为代表的数字加密货币中.自私挖矿攻击(Selfish mining)等挖矿攻击(Mining attack)策略威胁了采用工作量证明共识机制的区块链的安全性.在自私挖矿攻击策略被提出之后,研究者们进一步优化了单个攻击者的挖矿攻击策略.在前人工作的基础上,本文提出了新颖的两阶段挖矿攻击模型,该模型包含拥有单攻击者的传统自私挖矿系统与拥有两个攻击者的多攻击者系统.本文的模型同时提供了理论分析与仿真量化分析,并将两个攻击者区分为内部攻击者与外部攻击者.通过引入内部攻击者与外部攻击者的概念,本文指出传统自私挖矿系统转化为多攻击者系统的条件.本文进一步揭示了在多攻击者系统中两个攻击者将产生竞争并面临着“矿工困境”问题.攻击者间的竞争可被总结为“鲶鱼效应”:外部攻击者的出现导致内部攻击者的相对收益下降至多67.4%,因此内部攻击者需要优化攻击策略.本文提出了名为部分主动发布策略的全新挖矿攻击策略,相较于自私挖矿策略,该策略是半诚实的攻击策略.在特定场景下,部分主动发布策略可以提高攻击者的相对收益并破解攻击者面临的“矿工困境”问题.

关 键 词:区块链  比特币  工作量证明共识机制  挖矿攻击  自私挖矿

Catfish Effect Between Selfish Miners in Proof-of-Work Based Blockchain
RUAN Na,LIU Han-Qing,SI Xue-Ming.Catfish Effect Between Selfish Miners in Proof-of-Work Based Blockchain[J].Chinese Journal of Computers,2021,44(1):177-192.
Authors:RUAN Na  LIU Han-Qing  SI Xue-Ming
Affiliation:(School of Electronic Information and Electrical Engineering,Shanghai Jiao Tong University,Shanghai200240;Zhongyuan University of Technology,Zhengzhou 450007;Shanghai Key Laboratory of Data Science,School of Computer Science and Technology,Fudan University,Shanghai 201203)
Abstract:In the past decade,the consensus mechanism named proof of work has been widely applied by cryptocurrencies like Bitcoin.Though the security of a Proof of Work powered cryptocurrency is always the top priority,it is threatened by mining attacks like selfish mining.In 2014,Eyal proposed the first selfish mining model in a Proof of Work powered blockchain.Selfish mining is an irrational strategy so that the absolute value of the attacker’s reward will drop.However the ratio of the attacker’s reward to the other miner’s block reward would increase.Thus,the relative reward of the attacker is used to measure whether his attacking strategy is effective or not.Currently,the vast computational power in cryptocurrencies like Bitcoin and Ethereum makes it unrealistic to launch a selfish mining attack against them.But mining attack strategies are continuously optimized in recent years.After Eyal’s work,researchers have proposed many mining attack models with a single attacker.In these mining attack models,the attacker’s strategy space is extended and optimized via Markov decision process.The extension of the attacker’s strategy space is based on the assumption that the attacker is the only adversarial node in the blockchain network so that the strategy space of an attacker is still limited.In this paper,we propose a mining attack model with two attackers:the internal attacker and the external attacker.According to the attacker’s order of appearance,we divide the model into two phases:the traditional selfish mining system with the internal attacker and the multi-attacker system with the internal attacker and the external attacker.Our model provides both theoretical and quantitative analysis of how the traditional selfish mining system turns into the multi-attacker system.We prove that after the occurrence of the external attacker,both attackers will face a dilemma in the multi-attacker system:Both attackers’relative reward is less than expected.The unexpected competitions between the internal attacker and the external attacker,the overestimation of an attacker’s influence rate by himself and the auction like behavior of the internal attacker and the external attacker in the multi-attacker system are three leading causes of two attackers’dilemma.We name this phenomenon as Catfish effect in the multi-attacker system.The Catfish effect in the multi-attacker system leads to the consequence that the internal attacker or the external attacker has to optimize his attacking strategy.The internal attacker would overestimate his relative reward in the multi-attacker system by up to 67.4%after the existence of the external attacker.To break the dilemma faced by the internal attacker and the external attacker,we propose a novel mining strategy named Partial Initiative Release,which is a semi-honest mining strategy.An attacker makes his action based on Partial Initiative Release state machine.The most significant difference between Partial Initiative Release and selfish mining is that the attacker might act as an honest miner when he is at some certain state.In some specific situations,Partial Initiative Release allows the attackers to achieve a higher relative reward compared with selfish mining.
Keywords:blockchain  Bitcoin  proof-of-work  mining attack  selfish mining
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