private key
A secret 256-bit number that proves ownership of Bitcoin and authorizes transactions. Anyone with your private key controls your Bitcoin — never share it.
A private key is a randomly generated 256-bit number — so large that guessing one in use is statistically impossible. It is the foundation of Bitcoin ownership. From this single number, your public key and Bitcoin address are mathematically derived.
When you send Bitcoin, your wallet uses your private key to create a digital signature that proves you authorized the transaction, without ever revealing the key itself. This is the elegance of asymmetric cryptography: you can prove knowledge of a secret without exposing it.
The cardinal rule: your private key must remain private. If anyone else obtains it, they have full and irrevocable access to your Bitcoin. No customer support can help you. No password reset exists. This is the responsibility that comes with self-custody.