Public-Key Cryptography

How does it work?

Bob gives everyone a copy of his (public) locking key.  Alice uses it to lock a message, and sends the locked message to Bob.

Bob uses his (private) unlocking key to unlock the message.
Eve can't unlock it; she only has the locking key.
Neither can Alice!

So with this, Alice just needs to know Bob's public key in order to send him secret messages
These public keys can be published in a directory somewhere