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Pool and Centralization

Selfish Mining

Aka block-withholding. Don't annouce to network when a block is found. Keep working on the next block. If a second block is found, the network is fooled. Everyone in the network believes they are working on the longest chain, but you are. When the network finds a block, you broadcast your two secret blocks and make the network block invalid. While the entire network is working on the invalid block, you are competing with no one (free time).


  • Large players have incentives to mine unhonestly
  • Centralization -> Larger pool players cheat -> Smaller players kicked out -> More centralization
  • Measures against mining attacks:
    • Miners switch pools to prevent monopoly
    • Punish cheaters in protocol (very hard)
  • Comparing to mining attacks, double-spend attacks never occurred in the cryptocurrency history. Why? TODO.
  • Bitcoin is increasingly centralized, network safety dependent on very few large players