  It is widely accepted that Ethereum mining is highly centralized.
Nonetheless, centralization has been mostly characterized by exclusively
looking at the influence that independent miners or mining pools can have over
the network. Moreover, models of mining behavior assume that miners are either
unrelated or only relate via mining pools under highly structured and
transparent agreements. If these assumptions and the predictions they entail
were to be completely accurate, there would not be any evidence of on-chain
transactions between miners, other than the ones expected from mining pool
payouts. By looking at on-chain transactions between miners in the Ethereum
Network we find that aside from the payouts from mining pools to small miners,
there are also transactions that define relationships between mining pools,
independent miners and between independent miners and mining pools.
Furthermore, by characterizing the topology of the network of miner
transactions, we find the emergence of highly connected clusters that control
significant amounts of hashing power and exhibit relationships in the opposite
direction of what theoretical models predict. This more nuanced
characterization of mining centralization can help identify network
vulnerabilities and inform protocol redesigns.
