This is a basic https-like implementation using box.
Basic meaning that we have a concept of a client and server that have a secure session. A handshake is performed in which they trade public keys and begin a session. This utilizes public key encryption in that the sender uses the receiver's public key to encrypt the message. The receiver decrpyts the message with their corresponding private key.
To use this, we will use the prebuilt play-crypto binary.
First, start the server:
./play-crypto -s [-p <port>]
Next, connect as a client:
./play-crypto [-p <port>]