tweetnacl-box.js

const nacl = require('tweetnacl')
nacl.util = require('tweetnacl-util')

// generating Bob key pair
const bob = nacl.box.keyPair()
// generating Alice key pair
const alice = nacl.box.keyPair()

// generating one time nonce for encryption
const nonce = nacl.randomBytes(24)
// Bob encrypt message for Alice (only requires Alice public key)
const utf8 = 'Hello Alice'
const box = nacl.box(
  nacl.util.decodeUTF8(utf8),
  nonce,
  alice.publicKey,
  bob.secretKey
)
const message = {box, nonce} // somehow send this message to Alice

// Alice decrypt message from Bob (only requires Bob public key)
const payload = nacl.box.open(message.box, message.nonce, bob.publicKey, alice.secretKey)
// assert.equal(utf8, nacl.util.encodeUTF8(payload))