Pooled Mining is Driving Blockchains Toward Centralized Systems

The decentralization property of blockchains stems from the fact that each miner accepts or refuses transactions and blocks based on its own verification results. However, pooled mining causes blockchains to evolve into centralized systems because pool participants delegate their decision-making rights to pool managers. In this paper, we established and validated a model for Proof-of-Work mining, introduced the concept of equivalent blocks, and quantitatively derived that pooling effectively lowers the income variance of miners. We also analyzed Bitcoin and Ethereum data to prove that pooled mining has become prevalent in the real world. The percentage of pool-mined blocks increased from 49.91% to 91.12% within four months in Bitcoin and from 76.9% to 92.2% within five months in Ethereum. In July 2018, Bitcoin and Ethereum mining were dominated by only six and five pools respectively.