What Is A Public Key

From your private key, Bitcoin derives a public key.

The mathematical relationship between them is one-way. The private key generates the public key through a specific cryptographic process. But you cannot work backwards — given a public key, it is mathematically impossible to determine the private key that created it. The computation required would take longer than the age of the universe.

This one-way relationship is the foundation of Bitcoin’s security.

The public key can be shared freely. It’s public for a reason. It allows others to verify that a transaction was signed by the correct private key — without ever seeing the private key itself.

Think of it like a padlock and key. You can hand someone an open padlock — they can lock things with it, they can verify it’s yours. But they cannot use the padlock to make a copy of the key that opens it. The padlock is public. The key is private. Possession of one tells you nothing about the other.

In practice, most Bitcoin users never directly interact with their public key. Their wallet software handles the derivation automatically. But understanding that it exists — and that its relationship to the private key is mathematically irreversible — explains why Bitcoin’s security is so robust.

No server holds your keys. No company has a master copy. The security comes from mathematics, not from institutional trust.

Tomorrow: what is a Bitcoin address — the mailbox that anyone can send to.

— The Daily Bit