code: function deriveSharedSecret(ecdh, peer_b64_pubkey){
  	var shared_secret_src = ecdh.computeSecret(peer_b64_pubkey, "base64");
  	var shared_secret = crypto.createHash("sha256").update(shared_secret_src).digest().slice(0, 16);
  	return shared_secret;
  }
docs: --------------------------- sending/receiving messages