To put it simply, a bitcoin public address is the one you use to receive bitcoin, and a private address is the one you use to send them. Bitcoin public addresses appear as a random string of (around 30) alphanumeric characters, and begin with the numbers “1” or “3.”
Here’s an example of a public address: 1BQhEut2E4XmYm53Qt614NbrhBvuCoyxVc (click it to see its balance and transaction history on Blockchain.info)
Private addresses are usually longer, and start with the numbers “5” or “6.” You can show a public address/key to anyone you like, but make sure to keep the private ones well hidden! Bloomberg TV host Matt Miller famously learned this lesson the hard way in 2013, when he displayed a bitcoin paper wallet to the camera. A viewer scanned the image from his TV screen and took the funds.
Rather than forcing users to type out complex strings of characters, most bitcoin addresses appear as machine-readable QR codes. That’s why you often see bitcoiners appearing to photograph each others’ smartphone and laptop screens. It makes it much easier to pay quickly, especially in bars and restaurants.
Public and private addresses are also known as “keys”. If someone asks for either your public address or public key, show them the one starting with “1” or “3”. An address starting with “1” is a single-user address, whereas the “3” denotes a multi-signature (multisig) address. Multisig addresses can be held by more than one person, requiring more than one private key to release the funds.
With the advent of more sophisticated software wallets, private keys are becoming less visible to the user. However they still exist, and it doesn’t hurt to understand what they are and how they work.
Now that you know what public and private Bitcoin addresses are, you may have even more questions, such as:
Image via Wikimedia Commons