Private key: meaning in crypto

What is a private key

A private key is a secret code that proves you control the crypto held at a blockchain address and lets you sign transactions that move it.

Whoever has the private key controls the funds. A blockchain has no "forgot password" option, no help desk and no way to reverse a valid signed transaction. See blockchain for how the ledger records transfers.

Public key vs private key

Crypto uses a key pair: a private key and a public key.

The derivation works in one direction only. You can calculate the public key from the private key. You cannot calculate the private key from the public key or the address with any practical amount of computing power.

Worked example (hypothetical)

Ayesha keeps some coins in a self-custody crypto wallet on her phone, and she wants to send part of them to Bilal.

1. She enters Bilal's address and the amount in her wallet app.
2. The app uses her private key to create a digital signature for that specific transaction. The key itself never leaves the device.
3. The network checks the signature against her public key. If it matches, the transfer is valid and gets recorded on the chain.
4. Network fees are paid separately. On Ethereum these are gas fees.

Now suppose Ayesha saved her recovery words in a cloud notes app and someone gained access to that account. That person could rebuild her private key and send the coins anywhere. Nothing in the protocol can reverse that transfer.

Precise definition and edge cases

Formal definition. In elliptic-curve cryptography, used by Bitcoin, Ethereum and many altcoins, the private key is a randomly chosen secret number within the curve's valid range. The public key is a point on the curve computed from it.

Seed phrase. Most modern wallets are "hierarchical deterministic." They derive many private keys from a single seed, which is shown to the user as a list of recovery words. Losing the seed means losing every key derived from it.

Custodial accounts. On a centralised exchange, the exchange holds the private keys and you hold a claim on it. That is counterparty risk. See also custodian.

Multisignature. Some wallets need signatures from several keys before funds can move. This removes the single point of failure.

Hardware wallets. These keep the key on a separate device and sign transactions inside it.

Crypto CFDs. A crypto CFD at a broker such as Exness is a price contract. You hold no coins and no private key. Leveraged CFDs can lose money fast, and that risk has nothing to do with key security.

Where the term appears

• Wallet apps: "export private key," "back up recovery phrase," "never share your seed."
• DeFi apps: prompts to "sign" or "approve" a transaction with your wallet.
• News: exchange hacks, leaked keys, lost-key cases and court orders that cannot be enforced on-chain without the key.
• Scams: fake "support agents" or "wallet validation" sites that ask for your key or recovery words. A legitimate service never needs them.

Related terms

• Crypto wallet
• Blockchain
• Custodian
• DeFi
• CBDC
• Trading glossary

Frequent questions

Is a private key the same as a password?

No. A password can be reset by the service that issued it. A private key cannot be reset, and losing it means losing access to the funds.

Can someone find my private key from my wallet address?

Not in practice. The derivation only works one way.

What is the difference between a private key and a seed phrase?

The seed phrase is a human-readable backup that generates your private keys. Anyone holding it can recreate all of them.

Do I have a private key if I keep crypto on an exchange?

Usually not. The exchange controls the keys.

Does trading crypto CFDs involve a private key?

No. A CFD is a contract on the price, and you do not own the coin.