51% Attack
A 51% attack is majority control of proof-of-work block production that can enable recent reorganizations, double-spending, or transaction censorship.
Learn how digital-asset wallets, recovery phrases, cold storage, transaction nonces, and proof-of-work attacks affect control and settlement risk.
Digital-asset control depends on several systems that are often confused with one another. A Cryptocurrency Wallet manages signing authority, a Mnemonic Phrase may support recovery, and a Cold Wallet isolates keys through a controlled signing process.
Those custody mechanisms do not control the network itself. A Nonce can support transaction ordering or proof-of-work search, while a 51% Attack concerns who can dominate recent block production on a proof-of-work chain.
| Layer | Main question | Typical evidence |
|---|---|---|
| Keys and custody | Who can authorize a transfer, and how can access be recovered? | Key policy, wallet design, custody agreement, backups, approvals, and signing logs |
| Transaction processing | Was the intended transaction signed, broadcast, ordered, and confirmed? | Address, amount, network, nonce or input set, fee, transaction identifier, and receipt |
| Consensus and settlement | Which history does the network recognize, and how final is it? | Consensus rules, confirmations, validator or miner distribution, reorganization history, and finality controls |
A strong control at one layer does not repair a weakness at another. Cold storage cannot prevent a proof-of-work reorganization, and a high network hash rate cannot recover a lost private key.
Start by separating six questions:
This framework helps distinguish possession of credentials from legal ownership, displayed balances from segregated assets, and technical confirmation from irreversible economic settlement.
Digital assets can involve substantial market, custody, fraud, technology, legal, tax, and liquidity risk. These pages provide general education and do not recommend a wallet, custodian, token, transaction, or investment strategy.
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A 51% attack is majority control of proof-of-work block production that can enable recent reorganizations, double-spending, or transaction censorship.
A cold wallet isolates digital-asset private keys from internet-connected systems during ordinary storage and signing operations.
A cryptocurrency wallet manages private keys or signing access used to authorize transfers recorded on a blockchain or platform ledger.
A mnemonic phrase encodes wallet entropy in words so compatible software can derive a seed and recreate deterministic private keys.
A nonce is a context-specific value used once or in sequence to prevent replay, order transactions, or vary proof-of-work block headers.