Private key and public key: 256 bits decide who owns your coins

A private key is a secret number. Anyone who knows it can spend the coins held at an address. Anyone who does not cannot, no matter how much computing power they bring. The public key is its open counterpart: it is calculated from the private key, may appear anywhere and still gives the secret away. This one-way street is the whole trick behind Bitcoin and every other blockchain that works without a bank. Ownership in this system does not mean that a name sits in a register. Ownership means that someone can produce a valid signature.