This document provides an overview of public key cryptography. It introduces the concepts of public and private key pairs using the mailbox analogy. The key requirements for a public key scheme are that encryption and decryption must be easy with the appropriate key, but deriving the private key from the public key or decrypting without the private key must be computationally infeasible. Diffie-Hellman key exchange and RSA are described as examples of public key cryptography schemes. Potential attacks like man-in-the-middle are also discussed.