code: function generatePskSecret(ecdhForLocalDevice, remotePeerPublicKey,
                                    pskIdentityField) {
    var sxy = ecdhForLocalDevice.computeSecret(remotePeerPublicKey);
    return HKDF(module.exports.SHA256, sxy, pskIdentityField)
      .derive('', module.exports.AES_256_KEY_SIZE);
  }
docs: Generates a PSK secret between the local device and a remote peer.
  @param {ECDH} ecdhForLocalDevice
  @param {Buffer} remotePeerPublicKey
  @param {string} pskIdentityField
  @returns {Buffer}