We talked about how in cryptography you want your key to be complex so people can’t guess it.  Otherwise, why encrypt if they can figure out how to decrypt it easily?  We need another play to fix this. We’re going to talk about that other plan, it’s called Public Key Cryptography.

Public Key Cryptography means I have a public cryptography key.

Public Key

I can use that to encrypt anything I want, but I can’t use it to decrypt anything.  It’s like having a key to your house that will only lock doors, but not unlock them.  I can lock the house up when I leave, but there’s no way for me to get back inside.  This means I can share the key because there’s no worry that someone will break in using it.  In Public Key Cryptography, I share my public key with the world and they can encrypt things they want to send me.

Private Key

This is my private key, it’s purple because that’s my favorite color and this is my favorite key.  It’s the one I can use to unlock doors, or in encryption terms, I can use it to decrypt anything that’s encrypted with my public key.

This sounds pretty safe, right?  It’s actually used in something called Pretty Good Privacy so we’ll call it Pretty Safe Public Key Cryptography.  Well, not really, the real name doesn’t have Pretty Safe as part of it, but it’s still a good name.

It’s also used in web traffic.  If you go to a website using https:// rather than http://, you’re making a secure connection that encrypts your traffic.  That’s done using Public Key Cryptography, it’s just under the hood so you don’t see it.

Pretty cool, right?