Many encryption schemes are based on Public Key Encryption, or PKI. This form of encryption is based on complex mathematics, but the basic principal is quite simple: Everybody has two Keys.

Your first key can only be used to encrypt messages. This is your Public Key, and you can give it to anyone in the entire world. People can get your Public Key, encrypt a message with it, and then send it to everyone else in the world. But no one can read it, because the Public Key can only be used to encrypt messages, not decrypt them.

Your second key can only be used to decrypt messages. This is your Private Key, and you shouldn’t give it to anyone! People have already encrypted messages, and sent them out to everyone in the world. But, since you are the only one who has your Private Key, you are the only one who can decrypt it!

This is the basis of all Public Key Encryption, which is the most common form of encryption on the Internet. It’s used so often because it allows different parties to encrypt information to each other even if they’ve never met before, since each party can get the public key of the other party to send them an encrypted message.