Clear DefinitionsSelfish Mining
2 min read
Pronunciation
[sel-fish mahyn-ing]
Analogy
Imagine a group of treasure hunters who find a new part of a map leading to a big treasure (a new block) but keep it secret. They continue exploring based on their secret map extension, hoping to find even more treasure (more blocks on their private chain). If their secret map becomes longer and more detailed than the publicly known map, they can suddenly reveal their map, invalidating the progress others made based on the public map, and claim all the treasure they found secretly.
Definition
A malicious mining strategy in Proof-of-Work (PoW) blockchains where a miner or a group of colluding miners find a new block but deliberately withhold it from the rest of the network. They continue mining on their secret chain, hoping to make it longer. If their secret chain outpaces the public chain, they can then release their blocks, orphan the public chain's blocks, and claim more rewards or enable double-spending.
Key Points Intro
Key Points
A miner finds a block but does not broadcast it immediately.
They attempt to mine subsequent blocks on top of their secret block, creating a private chain.
If their private chain becomes longer than the public honest chain, they can publish it, causing a chain reorganization.
This can lead to increased revenue for the selfish miner (as honest miners waste effort on the orphaned chain) and potentially enable double-spends.
The viability of selfish mining depends on the miner's hashrate proportion and network conditions.
Example
A mining pool controlling a significant portion of the network's hashrate (e.g., >25-30%) might attempt selfish mining. If they find block 100, they keep it secret and start mining block 101. If the rest of the network finds and broadcasts an honest block 100, and the selfish miner then quickly finds their block 101, they can release both, orphaning the honest block 100.
Technical Deep Dive
Selfish mining strategies involve careful timing and decisions on when to reveal privately mined blocks based on the relative lengths of the secret chain and the public chain. The Eyal and Sirer paper (2013) formalized this attack and showed it could be profitable for miners with a certain threshold of hashrate, lower than the 51% required for direct block overriding. Network latency and connectivity play a role in its effectiveness. Countermeasures can include changes to fork-choice rules or encouraging better block propagation.
Security Warning
Selfish mining can undermine the fairness and security of a PoW blockchain by centralizing rewards and potentially destabilizing the network. While difficult to execute perfectly and often requiring substantial hashrate, it remains a theoretical concern for PoW systems.
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