Majority is not enough

By Ittay Eyal, Emin Gün Sirer. 2013

1,255 citations recorded by the source corpus.

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' revenue is larger than their fair share. The attack can have significant consequences for Bitcoin: Rational miners will prefer to join the attackers, 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 coalition 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 a coalition 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 coalition of any size can compromise the system.

Subfields: Artificial Intelligence, Information Systems

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Citations in the corpus

A Survey of Attacks on Ethereum Smart Contracts (SoK) (2017, background): “Despite some criticism about the effectiveness of the consensus protocol [37,44], recent theoretical studies establish its security whenever the honest nodes control the majority of the computational power of the network [39,52].”
REM: Resource-Efficient Mining for Blockchains (2017, background): “Despite their imperfections [26, 35, 37, 65, 71], blockchains [38, 64, 67] have attracted the interest of the financial and technology industries [16, 25, 34, 47, 69, 74] as a way to build a transaction systems with distributed trust.”
Secure High-Rate Transaction Processing in Bitcoin (2015, background): “Several papers have looked at incentive concerns related to the operation of the protocol, examining issues related to transaction propagation [6], selfish mining [8], and the distribution of rewards within mining-pools [15].”
SoK: Research Perspectives and Challenges for Bitcoin and Cryptocurrencies (2015, background): “Miller et al. [85] as well as Sirer and Eyal [111] have proposed " nonoutsourceable " puzzles that ensure whoever performs the mining work can claim the reward for themselves when a block is found, thus thwarting pools' enforcement mechanisms and making the formation of large pools between anonymous”
Bitcoin-NG: A Scalable Blockchain Protocol (2015, background): “Increasing block size improves throughput, but the resulting bigger blocks take longer to propagate in the network.”
Algorand: Scaling Byzantine Agreements for Cryptocurrencies (2017, background): “By relying on Byzantine agreement, Algorand eliminates the possibility of forks, and avoids the need to reason about mining strategies [8, 25, 46].”
Cryptocurrencies Without Proof of Work (2014, background): “Thus, an individual miner who has a fraction p of the total mining power can create each new block with probability ≈ p, though other factors such as “selfish mining” [1, 5, 6] can influence p.”
Permacoin: Repurposing Bitcoin Work for Data Preservation (2014, background): “When computational resources are allocated equally among individuals, cooperation according to Bitcoin’s reference implementation has been shown to be a Nash equilibrium, but not a unique one [13]; when an individual or coalition wields a third or more of the overall power, then it is more profitabl”
Blockchain's adoption in IoT: The challenges, and a way forward (2019, background): “However, authors in [69] prove that the malicious/dishonest miners resorting to selfish mining strategy can gain more revenue by only 25% of the total hashing power.”
Towards Scaling Blockchain Systems via Sharding (2018, background): “ time [52]. Recent works consider the system of rational and Byzantine nodes as opposed to honest and Byzantine nodes in BFT. Under this model, PoW is more vulnerable to attacks such as selsh mining [25]. 2.2 Intel Software Guard Extensions (SGX) Intel SGX [44] is a recently introduced set of CPU ex”
The Bitcoin Backbone Protocol: Analysis and Applications (2015, neutral): “[17]).”
A Survey on Ethereum Systems Security (2019, background): “This vulnerability was first reported in Reference [99], referring to that the assumption inherent to the Nakamoto consensus protocol—honest mining (i.”
Tendermint : Consensus without Mining (2014, background): “Recent work by Eyal and Sirer [6] showed that the Bitcoin protocol is susceptible to a minority collusion group that can grow to become a centralized majority.”
BLOCKBENCH: A Framework for Analyzing Private Blockchains (2017, background): “This probabilistic guarantee causes both security and performance issues: attacks have been demonstrated by an adversary controlling only 25% of the nodes [26], and Bitcoin transaction throughput remains very low (7 transactions per second [15]).”
SoK: Consensus in the Age of Blockchains (2017, background): “Selfish mining [40] allows selfish miners to generate more valid blocks than their computing power would normally allow them to if they were following the honest mining protocol.”