public-key cryptography

Public-key cryptography gives each person a matched pair of keys: a public key they can share freely, and a private key they keep secret. The two are mathematically linked so that what one key does, only the other can undo. This solves a problem that stumped people for centuries — how to communicate securely with someone you have never met and never shared a secret password with.

The pair works two complementary ways. For privacy, anyone can use your public key to lock a message that only your private key can open, like a mailbox with a slot the whole world can drop letters into but only you have the key to empty. For proof of identity, you use your private key to sign something, and anyone can use your matching public key to verify the signature is really yours — without ever learning the private key itself.

On a blockchain this is the foundation of ownership. Your account is essentially a public key (often shortened into an address), and control over its funds is simply control over the matching private key. To send coins you sign the transaction with your private key; the whole network checks it against your public key and accepts it as authentically yours. No bank account, no password reset, no middleman — whoever holds the private key holds the funds.