Private key
A private key is a secret number that gives full control over the coins at an address. Whoever knows the key can sign transfers and move the funds.
How it works
A private key is a huge random number (256 bits in Bitcoin and Ethereum). A public key is derived from it mathematically, and an address from the public key. It does not work in reverse: you cannot work out the key from the address.
When you send coins, your wallet signs the transaction with the private key. The network checks the signature and knows the owner approved the transfer. The key itself is never sent to the network.
Usually you never see the key directly: the wallet generates it from your seed phrase. One seed phrase can produce many keys and addresses, which is why leaking the seed phrase is even worse than leaking a single key.
Never show your key or type it into websites.
You kept your key in your phone notes, and the notes synced to the cloud. If the cloud account is hacked, the attacker imports the key into any wallet and moves all your coins. That transfer cannot be reversed.
The main mistake is storing the key or seed phrase digitally: a screenshot, notes, cloud storage or a message to yourself. Malware and account hackers steal exactly these files. Write your seed phrase on paper or metal and keep it offline, and for larger amounts use a hardware wallet, where the key never leaves the device. Also remember: if the exchange holds the key instead of you, the exchange is the one actually in control of the coins.
Questions and answers
What is a private key in simple terms?
It is the secret password to your coins, just very long and randomly generated. Anyone who knows it can send your coins anywhere.
What is the difference between a private key and a seed phrase?
A seed phrase is 12 or 24 words that the wallet uses to generate private keys. A key controls one address, while the seed phrase controls every address in the wallet.
Can I recover a lost private key?
Only from your seed phrase or a wallet backup. If you have neither, access to the coins is lost forever, and no support team can bring it back.
Related terms
Read next
Your seed phrase gives full access to a wallet. Where to keep it and what never to do.
Read →Wallet security: 10 rulesA short list to check your own defences.
Read →Public keyA public key is a number derived from your private key that is safe to share. The network uses it to verify…
Updated: 2026-10-19