Ataque de 51%
Um ataque de 51% acontece quando uma entidade controla mais da metade do poder de mineração de uma blockchain.
The feasibility of a 51% attack depends heavily on the total hash rate of the network. On a small, niche PoW chain with low total mining power, an attacker could potentially rent enough hash power (via services like NiceHash) to execute the attack for a few hours. On a major network like Bitcoin, the physical acquisition of enough ASICs (Application-Specific Integrated Circuits) and the necessary electricity would cost billions of dollars, making the attack financially irrational—the attacker would essentially destroy the value of the network they just invested billions in to control.
graph LR
Center["Ataque de 51%"]:::main
Pre_consensus_mechanisms["consensus-mechanisms"]:::pre --> Center
click Pre_consensus_mechanisms "/terms/consensus-mechanisms"
Pre_proof_of_work["proof-of-work"]:::pre --> Center
click Pre_proof_of_work "/terms/proof-of-work"
Pre_proof_of_stake["proof-of-stake"]:::pre --> Center
click Pre_proof_of_stake "/terms/proof-of-stake"
Rel_double_spending["double-spending"]:::related -.-> Center
click Rel_double_spending "/terms/double-spending"
Rel_sybil_attack["sybil-attack"]:::related -.-> Center
click Rel_sybil_attack "/terms/sybil-attack"
Rel_hard_fork["hard-fork"]:::related -.-> Center
click Rel_hard_fork "/terms/hard-fork"
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🤓 Expert Deep Dive
Technically, a 51% attack is an exploit of the Nakamoto Consensus 'Longest Chain Rule'. When an attacker controls >50% hashrate, they can generate a private version of the blockchain faster than the rest of the network combined. By keeping this fork secret and then 'releasing' it once it is longer than the public chain, the network is forced to follow the attacker's chain due to the rules of 'Chainwork'. This results in a 'Chain Reorganization' (reorg). The primary damage is the ability to 'Double-Spend' by broadcasting a transaction on the public chain, waiting for confirmation, then releasing the private chain where that transaction never happened.