What Is a 51% Attack and How Does It Specifically Enable Double-Spending?
A 51% attack occurs when an entity controls more than half of a blockchain network's mining hash rate. This control allows them to reorganize the transaction history and prevent new transactions from gaining confirmation.
Double-spending is achieved by sending a transaction to an exchange (e.g. selling coins) and then using the majority hash power to mine an alternative, private chain that excludes the original transaction, effectively 'undoing' the payment and retaining the coins.
Glossar
Majority Hash Power
Dominance ⎊ Majority hash power refers to the concentration of computational resources controlled by a single entity or cartel, representing the ability to unilaterally confirm or reject transactions on a proof-of-work network.
Private Chain
Chain ⎊ A private chain, within the context of cryptocurrency derivatives, represents a permissioned blockchain network operating independently of public, decentralized infrastructures like Ethereum or Bitcoin.
Transaction History
Historical Record ⎊ Transaction History is the complete, ordered sequence of all validated transfers and smart contract interactions associated with a specific public address or the entire blockchain ledger, forming the immutable audit trail.