Private Key

A private key is the secret number that controls a cryptocurrency address — whoever knows it can spend the funds, and no one without it can. It is an enormous randomly generated number (for Bitcoin and Ethereum, 256 bits), from which the public key and address are mathematically derived. The math only works one way: the address can be computed from the private key, but the private key cannot be recovered from the address.

When you send crypto, your wallet uses the private key to create a digital signature over the transaction. The network verifies the signature against your public key, confirming you authorized the payment without the key ever being revealed. Modern wallets generate all your private keys from a single seed phrase — the 12 or 24 words you back up at setup — so protecting that phrase protects every key. For example, if your phone is destroyed, entering the seed phrase into a new wallet regenerates the same private keys and restores full access to your funds.

A common misconception is that exchanges or wallet companies can reset your access the way a bank resets a password; with self-custody there is no recovery mechanism, and a lost private key (and lost seed phrase) means the funds are permanently frozen on-chain. The security rules are absolute: never share a private key or seed phrase with anyone, never type them into websites, and be aware that any "support agent" asking for them is running a scam.