Charles wants to encrypt his email communications. How can he do that? Leo says that your email can go through dozens of servers before getting to the person you addressed it to. And everyone along the way can read it unless it's encrypted. It's more like a postcard, but without federal privacy protection. PGP (Pretty Good Protection) uses public-key cryptography, which has two different keys. One public, and one private. Only you can encrypt with the private key, while the public key is used to verify and open the email. You can give the public key to anyone.