Public key

A public key is a cryptographic key derived from your private key. You use it to receive funds and to let the network verify your signatures. As the name says, it is meant to be seen. Sharing it gives nothing away.

The two keys form a pair. The maths flows one direction. Your wallet generates the public key from the private key in an instant, but no computer can run that backwards to recover the private key from the public one. That gap is what keeps the system standing.

Here is how the pair works day to day. When you spend, your wallet signs the transaction with the private key. Every other computer on the network then checks that signature against your public key. If it matches, the transaction is valid. The private key proves ownership without ever being revealed; the public key does the checking out in the open.

In practice you rarely hand out the raw public key. Most chains run it through a hashing step to produce a shorter wallet address, the string you actually paste when someone sends you coins. A Bitcoin address is around 26 to 42 characters. That address is the public-facing front of your key pair.

One point trips people up. Because the public key and the address are derived from the private key, anyone watching the blockchain can see the balance and history tied to an address. They can look. They cannot move anything. Only the private key can authorise a spend.

So treat the two keys differently. The public key and address are for sharing, like an email address you give out to receive post. Keep the private key buried. Both come from the same source, but only one is a secret.