Majority Is Not Enough: Bitcoin Mining Is Vulnerable

  • Ittay EyalEmail author
  • Emin Gün Sirer
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 8437)


The Bitcoin cryptocurrency records its transactions in a public log called the blockchain. Its security rests critically on the distributed protocol that maintains the blockchain, run by participants called miners. Conventional wisdom asserts that the mining protocol is incentive-compatible and secure against colluding minority groups, that is, it incentivizes miners to follow the protocol as prescribed.

We show that the Bitcoin mining protocol is not incentive-compatible. We present an attack with which colluding miners obtain a revenue larger than their fair share. This attack can have significant consequences for Bitcoin: Rational miners will prefer to join the selfish miners, and the colluding group will increase in size until it becomes a majority. At this point, the Bitcoin system ceases to be a decentralized currency.

Unless certain assumptions are made, selfish mining may be feasible for any group size of colluding miners. We propose a practical modification to the Bitcoin protocol that protects Bitcoin in the general case. It prohibits selfish mining by pools that command less than \(1/4\) of the resources. This threshold is lower than the wrongly assumed \(1/2\) bound, but better than the current reality where a group of any size can compromise the system.


Overlay Network Sybil Attack Honest Node Mining Power Mining Pool 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



We are grateful to Raphael Rom, Fred B. Schneider, Eva Tardos, and Dror Kronstein for their valuable advice on drafts of this paper, as well as our shepherd Rainer Böhme for his guidance.


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Copyright information

© International Financial Cryptography Association 2014

Authors and Affiliations

  1. 1.Department of Computer ScienceCornell UniversityIthacaUSA

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