What Is a Public Key in Crypto? The Address You Can Share

A public key is the half of your crypto wallet you are meant to give away. Your wallet address, the long string starting with bc1 on Bitcoin or 0x on Ethereum, is made from it. Anyone can use that address to send you coins, and nobody can take anything out with it. Sharing it is safe.

Where does a public key come from?

A wallet such as MetaMask or a Ledger device starts by creating a private key: one enormous secret number. From that number it calculates a public key, and from the public key it shortens down to the address you copy and paste. The maths only runs one way. Going from the private key to the address takes an instant; going backwards from the address to the private key is, as far as anyone knows, impossible. That one-way street is what lets you publish one half and hide the other.

Why not just call it an address?

Picture a glass mailbox bolted to the street. Everyone walking past can read the number on the front, drop letters in, and even see how full it is. Only the key in your pocket opens the door. The number on the front is your public key and address; the key in your pocket is your private key. The two words get used loosely, and in day-to-day use the address is the thing you actually paste into an app.

What can other people do with it?

Send to it, and look. Every payment ever made to a Bitcoin or Ethereum address is public, and anyone can type an address into a block explorer and read its whole history. There is no name attached, but there is no privacy either once someone connects an address to you. Bitcoin wallets quietly make a fresh address for every payment to blunt this. Ethereum accounts usually reuse one address, so everything that account has ever done sits in plain view.

One habit is worth building: before you send anything real, check the first and last four characters of the pasted address against the original, then send a tiny test amount first. Some malware swaps addresses on your clipboard, and the check costs seconds. Next, read what a private key is and how the shared ledger keeps score.