The Bitcoin whitepaper is clear about Bitcoin’s core feature: it is permissionless. Anyone in the world can pay anyone by joining the peer-to-peer network and broadcasting a transaction. Proof of Work consensus even empowers anybody to become a block producer, and means that the only way to reverse a payment is to overpower everyone else through hashpower.

But Proof of Work only defines how to choose a winner amongst competing chains; it does not help a node discover it. A 51% attack – or a 100% attack – is much easier if an attacker can prevent nodes from hearing about competing chains. The job of discovery belongs to the peer-to-peer module, which juggles many contradictory…

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