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关于比特币中BWH攻击的一个注记
程恒喆,冯秀涛
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(中国科学院数学与系统科学研究院 数学机械化重点实验室, 北京 中国 100190;中国科学院大学, 北京 中国 100190)
摘要:
比特币是当前信息安全应用研究领域的热点问题之一.在比特币所采用的PoW共识协议中,挖矿具有重要作用.在现实生活中,矿工为获得更多的奖励,往往聚集成矿池,以达到在挖矿中获取更高算力进而获取更多区块奖励的目的.针对比特币矿池,Meni Rosenfeld首次提出了一种称为BWH攻击的攻击方式,Loi Luu等人进一步从理论上证明了相对于诚实挖矿,攻击者通过实施BWH攻击可以获得更高的收益.在本文中,我们分析了BWH攻击的理论基础,发现Loi Luu等人关于BWH攻击的理论分析中存在的一个错误,即Loi Luu等人忽略了整体算力改变对系统产生区块所需时间的影响,从而导致其所对比的关于攻击者实施BWH攻击所获得的收益与不实施攻击所获得的收益,实际上是在不同时间长度下的收益对比.显然这种对比缺乏合理性.在相同时间长度下,我们进一步讨论了攻击者实施BWH攻击与不实施攻击所获得的收益对比,得到了与Loi Luu等人完全相反的结论,即相对诚实挖矿来说,攻击者实施BWH攻击反而获得了相对较少的收益.因此攻击者缺乏实施BWH攻击的动机,除非其纯粹出于破坏矿池的目的而采用BWH攻击.
关键词:  比特币  区块链  矿池  BWH攻击
DOI:10.19363/j.cnki.cn10-1380/tn.2018.05.05
投稿时间:2018-02-16修订日期:2018-04-28
基金项目:国家自然科学基金项目(No.11688101)以及北京太一云科技有限公司资助。
A Note on Block Withholding Attack on Bitcoin
CHENG Hengzhe,FENG Xiutao
Key Laboratory of Mathematics Mechanization, Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing 100190, China;University of Chinese Academy of Sciences, Beijing 100190, China
Abstract:
Bitcoin is one of the hot issues in the application of information security. Mining plays an important role in the PoW protocol which is used in Bitcoin. In the real world, miners tend to gather into mining pools to get higher hash power and more rewards. Against mining pools, Meni Rosenfeld first proposed an attack called BWH attack, which is a kind of attack on Bitcoin pools. Loi Luu et al. gave a theoretical analysis of BWH attack and proved that the attacker could gain more rewards by implementing BWH attack than that got by mining honestly. In this paper, we analyze the theoretical basis of BWH attack and find a flaw in Loi Luu et al.'s theoretical analysis of BWH attack. Namely, Loi Luu et al. ignored the effect of changing hash power on the amount of time required for Bitcoin systems to generate a block. So Loi Luu et al. indeed compared the revenue from performing BWH attack and non-implementation attack over different length of time, which is clearly not justified. At the same length of time, we further discuss the revenue acquired by attacker in implementing BWH attacks versus non-implementation, and have an opposite conclusion to Loi Luu et al, that is, comparing with mining honestly, the attacker receives less revenue by implementing BWH attack. Therefore, the attacker lacks the motivation to implement BWH attack unless they use BWH attack solely for the purpose of damaging the mining pool.
Key words:  bitcoin  blockchain  mining pools  BWH Attack