Selfish Mining

Selfish mining is a Bitcoin mining strategy where a miner withholds newly found blocks to gain more than their fair share of block rewards.

This concept was described in a 2013 paper by Cornell researchers Ittay Eyal and Emin Gun Sirer, titled "Majority Is Not Enough: Bitcoin Mining Is Vulnerable." The authors argued that the mining incentives designed to keep proof of work miners honest can, in theory, be gamed.

Normally, a miner announces a block as soon as they find it, and if the network confirms it, they collect the block reward.

A selfish miner instead withholds newly found blocks, building a private branch of the chain while the rest of the network keeps working on the public one.

The goal is to stay at least one block ahead of the network. Because nodes accept the chain with the most accumulated proof of work as valid, the selfish miner can reveal their longer private chain at a chosen moment. 

When they do, the competing public blocks are discarded, their transactions are reversed, and the selfish miner collects the rewards while other miners have wasted their resources.

The success of selfish mining depends partly on luck but mainly on the miner’s share of network hash rate. Research suggests the strategy can become potentially profitable once a miner controls a large portion of total hashing power, with theoretical models often citing a threshold of 25% or higher. Actual feasibility also depends on network propagation speed and how other miners respond.

Over time, selfish mining could concentrate hashing power into fewer pools and weaken the decentralization that secures Bitcoin, a concern related to the broader risk of a 51% attack. In practice, many observers remain skeptical that it could severely damage Bitcoin, since centralizing the network in this way would undermine the value of the very asset the miner earns rewards in. This means it would be in most miners’ best interests to act honestly.

Learn more: Selfish Mining Explained