Public key

The public key is the counterpart of the private keyGlossaryPrivate keyA secret, randomly generated number that you use to sign transactions and so control your bitcoin. Anyone who knows the private key can spend the bitcoin that belongs to it – it must never fall into anyone else’s hands.On the learning path: Stage 5 · Step 3 – Backing up your seed phrase →In the glossary →×. Your wallet calculates it using elliptic-curve mathematics (curve secp256k1); in the usual compressed form, it is 33 bytes long.^[1]

What it’s for

Bitcoin are tied to a public key. Only someone who signs with the matching private key can spend them – and every node uses the public key to check that the signature is genuine. The whitepaper already describes it this way: the previous owner signs, among other things, the public key of the next one.^[2]

Usually you only need to share a Bitcoin addressGlossaryBitcoin addressA string of characters like ‘bc1q…’ that someone can send bitcoin to. It is usually derived from a public key, can be shared without risk to your funds and should be generated afresh for every payment.On the learning path: Stage 5 · Step 4 – First withdrawal →In the glossary →× derived from it. Older addresses (1…) and SegWit addresses (bc1q…) generally contain a hash of the key; Taproot addresses (bc1p…) contain a public key calculated from it directly.^[3]

What you should know

• No access to your funds: with today’s technology, nobody can spend your bitcoin with a public key.
• It isn’t private: anyone who knows it or your addresses can trace on the blockchain which amounts belong to them. That’s why good wallets use a new address for every payment.
• Take care with your xpubGlossaryxpub (extended public key)An extended public key from which all the addresses of a wallet account can be calculated. Nobody can spend bitcoin with it – but anyone who knows it can see your entire account history.In the glossary →×: all the addresses of a wallet account can be derived from this extended public key. Anyone who has it can see your balance and every future payment to it.