What is a private key?
- Author
- CRYPTO PORT Editorial
- Published
- Updated
- Reading time
- 5 min
In short
A private key is the number that grants the power to move assets on a blockchain. Whoever holds it is treated as the owner, so the moment someone else learns it, the funds are theirs to take. Nearly all of crypto security comes down to protecting this one value.
Key points
- The only value that can sign a transfer
- Once exposed, funds cannot be recovered
- Addresses are derived one-way from it
- Lose it and the assets are frozen forever
Definition
A secret number used to sign blockchain transactions. The signature lets the network verify that a transfer really came from the rightful owner.
A private key is really just a very large random number — 256 bits on Bitcoin and Ethereum, roughly a 77-digit decimal. The public key is computed from it, and the receiving address from that. The maths runs one way only: you cannot work backwards from an address to the key.
To send funds, you sign the transaction with the key. Other participants verify the signature using the public key, and never need to see the private key itself. In effect you prove you hold the key without revealing it.
A wallet app simply stores this key on your device and signs with it on demand. People say coins are 'in' a wallet, but the coins live on the chain — the wallet holds the key. When you leave funds on an exchange, the exchange holds the key, not you.
Watch out for
- · Any screen asking you to type a private key or seed phrase should be treated as fraud, however official it looks
- · Screenshots and cloud notes turn one device compromise into total loss
- · No support desk can restore a lost key — there is no operator who can