What Is the Significance of “Longest Chain Rule” in a 51 Percent Attack?
The "longest chain rule," a fundamental consensus mechanism in PoW, dictates that the blockchain with the most cumulative proof-of-work (i.e. the longest chain) is the valid one. An attacker with 51 percent control can mine blocks faster than the rest of the network combined.
They secretly build a private chain, and when it surpasses the length of the public chain, they release it. The network then automatically switches to the attacker's chain, accepting its history, which includes the attacker's fraudulent transactions.
Glossar
Consensus Mechanism
Validation ⎊ Consensus mechanisms, within cryptocurrency, represent the procedural logic ensuring state agreement across a distributed network, critical for preventing double-spending and maintaining data integrity; their design directly impacts network security and scalability, influencing transaction throughput and finality times, particularly relevant in decentralized finance applications.
Soft Fork
Upgrade ⎊ This refers to a backward-compatible change to the protocol’s software, where non-upgraded nodes will still recognize blocks produced by upgraded nodes as valid, allowing for gradual adoption of new features or bug fixes.
Chain Reorganization
Blockchain Fork Resolution ⎊ The process by which a network resolves a temporary divergence in the transaction history, typically resulting in the abandonment of the shorter chain in favor of the one with greater cumulative proof-of-work.
Longest Chain Rule
Consensus Rule ⎊ Longest Chain Rule is the fundamental protocol mechanism dictating that in the event of a temporary fork, the chain exhibiting the greatest cumulative proof of work or stake is recognized as the canonical and valid history, thus finalizing transactions.
Hard Fork
Disruption ⎊ A hard fork represents a radical divergence in a blockchain’s protocol, creating a permanent split and typically resulting in a new cryptocurrency.
Longest Chain
Consensus ⎊ The longest chain rule is the core mechanism for achieving consensus in Proof-of-Work systems like Bitcoin.