Send messages

Before we start, the obligatory immature cryptography warning.

Please, don’t depend on our code for strong privacy (yet). We are still at an early stage.

Having said that, we are aiming to bring very strong privacy guarantees to users and service providers, and you want to see how it works. So let’s dance.

This quickstart demonstrates how you can use Nym from webassembly-capable browser or mobile apps. Other languages are supported via a Rust client which exposes a websocket to give you the same functionality as what we explain here - so if you want to write a Nym app in any server-side language (Python, JavaScript, C#, Java, Scala, etc) you can do that. See the Build Privacy Applications section of the docs for more information.


Install npm for your platform. Then, from the top-level nym directory:

cd clients/webassembly/js-example
npm install
npm run start

This will install the Nym webassembly client and start a local webserver on http://localhost:8001.

It’s a simple chat interface, allowing you to enter a recipient address and send a message. We’ll try it out in a moment, but before we do, it makes sense to talk about addressing, and the concept of Nym identities, so you can understand what an address is.

Nym identities

Nym identities are denoted a bit like email addresses. But instead of being user@host, a Nym identity is user-public-key@gateway-public-key.

When the demo code loads, a new Nym identity is constructed, and its public key is put into the text field labelled Sender. This identity is regenerated each page load to keep the demo as simple as possible - it’ll look something like:


Note that there’s an @ in the middle. Your address will be different, but it will have the same format.

In my example, everything before the @, i.e. 71od3ZAupdCdxeFNg8sdonqfZTnZZy1E86WYKEjxD4kj is the public key of our Nym identity.

Everything after the @, i.e. FWYoUrnKuXryysptnCZgUYRTauHq4FnEFu2QGn5LZWbm is the public key of a Nym gateway where messages will be received for this identity.

Sending mixnet messages using JavaScript and WebAssembly

The simplest demo: send a packet through the mixnet to yourself. Copy the entire contents of the Sender field into the Recipient field. Then press the Send button.

send a packet

The message in the Message field is wrapped up in Sphinx layer encryption, mixed with other peoples’ traffic, bounced all over our glorious planet, and routed back to your browser window.

To create and send to another identity, open up another browser tab at http://localhost:8001. Copy the Sender from one of your browser windows into the Recipient of the other, and you’ll be able to send information back and forth.

Now let’s look at the code.

User interface

The HTML user interface is simple, ugly, and effective (if you have UI skills and want to help a privacy project, please get in touch!). It looks like this:

<!DOCTYPE html>
<html lang="en">

  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Nym WebAssembly Demo</title>

    <label>Sender: </label><input disabled="true" size="85" type="text" id="sender" value="">

    <label>Recipient: </label><input size="85" type="text" id="recipient" value="">
    <label>Message: </label><input type="text" id="message" value="Hello mixnet!">
    <button id="send-button">Send</button>

  <p>Send messages from your browser, through the mixnet, and to the recipient using the "send" button.</p>
  <p><span style='color: blue;'>Sent</span> messages show in blue, <span style='color: green;'>received</span>
    messages show in green.</p>

    <span id="output"></div>
  <script src="./bootstrap.js"></script>



Nothing too thrilling here - we define user interface controls with ids sender, recipient, message and send-button, then load our JavaScript.


We’re depending on the @nymproject/nym-client-wasm npm package in package.json:

  "dependencies": {
    "@nymproject/nym-client-wasm": "^0.7.4"

Choose the highest SemVer patch version for the Nym network version you’re connecting to. E.g. if most Nym nodes in the dashboard are running 0.7.something, pick the newest 0.7.x release from the nym-client-wasm npmjs page.

In our index.js, we import the Nym Client and Identity:

import {
} from "nym-client-wasm/client"

An Identity is a cryptographic identity containing a public/private keypair, and a gateway address.

The Client is a network wrapper which talks to a Nym gateway server over a websocket.

Let’s see them in action. This is a mixnet client in JavaScript:

async function main() {
    // Set up identity and client
    let directory = "";
    let identity = new Identity();
    let nymClient = new Client(directory, identity, null);

    // Wire up events callbacks
    nymClient.onConnect = (_) => displaySenderAddress(nymClient);
    nymClient.onText = displayReceived;
    nymClient.onErrorResponse = (event) => alert("Received invalid gateway response",;

    // Start the Nym client. Connects to a Nym gateway via websocket.
    await nymClient.start();

    // Wire up the `send` button
    const sendButton = document.querySelector('#send-button');
    sendButton.onclick = function () {

It’s not complex, but let’s take it piece by piece.

let directory = "";    // 1
let identity = new Identity();                         // 2
let nymClient = new Client(directory, identity, null); // 3

In line 1, the variable directory is a URL pointing at a Nym network instance (in this case, our QA network). The Nym directory holds IP address and public key info for Nym mixnodes, validators, and gateways. See the mixnet docs for more on this.

Line 2 creates a new Identity object.

Line 3 initializes a new Nym Client using the given directory and identity. The third parameter, authToken, is null.

At this point, we’ve got a nymClient instance. When we tell the client to start(), it will connect to the Nym gateway via a websocket. But if we connect right now, we won’t see anything in our application. We need to wire the client to our user interface.

Let’s configure nymClient to connect it to our UI.

When we connect to the Nym gateway, we will want to display the sender address (i.e. our own address) in the Sender text field. The callback onConnect lets us trigger our own actions. When we receive messages from the mixnet, we want to display them in our user interface. And if we get an error when attempting to connect, we’ll use good old fashioned alert() to display it.

nymClient.onConnect = (_) => displaySenderAddress(nymClient);
nymClient.onText = displayReceived;
nymClient.onErrorResponse = (event) => alert("Received invalid gateway response",;

Clicking the Send button should send our message.

const sendButton = document.querySelector('#send-button');
sendButton.onclick = function () {

Finally, we can start the client:

await nymClient.start();

At this point, a lot of things happen.

  1. The nymClient talks to the defined directory and asks it for a list of currently running gateways, mixnodes, and validators. We call this the network topology.
  2. Once it has the network topology in hand, nymClient connects to the first gateway it finds, via a websocket connection.
  3. As noted previously, our nymClient was initialized without an authentication token. So it registers an account on the gateway, and gets back an authentication token in response. In a real application, we’d save that authtoken so we could use it to talk to the gateway later.

Now that nymClient is registered, we can send messages over the mixnet.

Sending a packet

We’ve already wired our sendButton.onClick to the function sendMessageTo(client). Here’s what it looks like:

function sendMessageTo(nymClient) {
    var message = document.getElementById("message").value;
    var recipient = document.getElementById("recipient").value;
    nymClient.sendMessage(message, recipient);

The interesting line here is nymClient.sendMessage(message, recipient). The client takes the message and the recipient from the user interface and calls sendMessage. The Nym client JavaScript talks to a webassembly binary which does layer encryption of a Sphinx packet. The client then sends this encrypted binary blob up the websocket connection to the Nym gateway.

The gateway translates to/from IPv4/IPv6 if necessary, and forwards the Sphinx packet to the mixnet. The packet then traverses the mixnet through multiple hops, with one layer of encryption being stripped each time.

After exiting the mixnet, still encrypted in Sphinx, the packet reaches the destination gateway. If the recipient that the packet is addressed to is currently online, the packet will be delivered immediately. If the recipient is offline, the packet will be stored until the user comes online, and then delivered.

Sphinx packet creation

Clients create Sphinx packets. These packets are a bit complicated, but for now all you need to know is that they have the following characteristics:

  1. they consist of a header and a body
  2. the header contains unencrypted routing data
  3. bodies are encrypted
  4. bodies are padded so that they’re all the same size
  5. observers can’t tell anything about what’s inside the encrypted body
  6. the body is layer-encrypted - it may contain either another sphinx packet or a payload message


Anonymous replies are possible using Single Use Reply Blocks, or SURBs. They don’t yet exist in the WebAssembly client, but should be available in the next release.

Why would you want SURBs? It’s useful to be able to reply to someone without necessarily knowing who they are. Keep in mind, recipients are not necessarily people: they can be privacy-respecting Service Providers, or people. SURBs allow Service Providers to respond to users without knowing who they are.


Sending JSON is totally possible, just stick it into the message box and send it (or send it programmatically if you’re writing an application of your own).

Further reading

So far, we’ve just scratched the surface. See the Build Privacy Applications docs for a discussion of anonymous replies, key storage, running mixnodes, writing Service Providers, and using other languages to talk to the mixnet.

If you run into trouble, please ask for help in the channel nymtech.friends#general on KeyBase.