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MicroMix: A noncustodial Ethereum mixer

This is the monorepo for all code and documentation for a noncustodial Ethereum mixer. Try it at

Join the Telegram group to discuss.

A mixer moves ETH or ERC20 tokens from one address to another in a way that nobody except the sender can know for sure that these addresses are linked. This mixer lets a user deposit fixed amounts of ETH into a contract, and when the pool is large enough, anonymously submit zero-knowledge proofs which show that the submitter had previously made a deposit, thus authorising the contract to release funds to the recipient.

As a transaction relayer pays the gas of this transaction, there is no certain on-chain connection between the sender and recipient. Although this relayer is centralised, the mixer is noncustodial and no third party can exit with users' funds.

A technical specification of the mixer is here.

This mixer is highly experimental and not yet audited. Do not use it to mix real funds yet. It only supports Kovan ETH for now. Get Kovan ETH from a faucet here or here.

Supported features

The current version of this mixer is a simple MVP for desktop Chrome, Brave, or Firefox. You should also have MetaMask installed, and some Kovan ETH. You need at least 0.11 KETH to mix 0.1 ETH, and 20 Kovan DAI and 0.01 ETH to mix Kovan DAI. You can generate Kovan DAI using MakerDAO's CDP creation tool here.

It has the following features:

  1. A user interface which allows:

    • One deposit per day.

    • One-click withdrawal once UTC midnight has passed.

    • Immediate self-withdrawals in case the user wants their funds back at the cost of privacy.

    • Immediate withdraw requests if the user wishes the operator to mix the funds immediately, which also comes at the cost of some privacy.

  2. A backend server with one JSON-RPC 2.0 endpoint, mixer_mix(), which:

    • Accepts, verifies, and submits a zk-SNARK proof (generated in the user's browser) to the mixer contract.
  3. Ethereum contracts:

    • The Semaphore zero-knowledge signalling system as a base layer.

    • A Mixer contract with functions which

      • Accepts ETH or ERC20 token deposits.

      • Accepts mix requests. Each request comprises of a zk-SNARK proof that a deposit had been made in the past and has not already been claimed. If the proof is valid, it transfers funds to the recipient and takes an operator's fee.

      • Allows the operator to withdraw all accurred fees.

    • Gas costs after the Istanbul network upgrade is currently 1.2 million per deposit and 378k per withdrawal. The gas cost for each withdrawal (before Istanbul) is 886k.

Local development and testing

These instructions have been tested with Ubuntu 18.0.4 and Node 11.14.0.


  • Node v11.14.0. - We recommend nvm to manage your Node installation.

  • etcd v3.3.13

    • The relayer server requires an etcd server to lock the account nonce of its hot wallet.

Local development

Install npx and http-server if you haven't already:

npm install -g npx http-server

Clone this repository and its semaphore submodule:

git clone && \
cd mixer && \
git submodule update --init

Download the circuit, keys, and verifier contract. Doing this instead of generating your own keys will save you about 20 minutes. Note that these are not for production use as there is no guarantee that the toxic waste was discarded.


Create a file named hotWalletPrivKey.json in a location outside this repository with a private key which will serve as the operator's hot wallet. The following private key corresponds to the address 0x627306090abab3a6e1400e9345bc60c78a8bef57, the first Ethereum address which can be derived from the well-known candy maple cake sugar... mnemonic. Don't use this in production.

    "privateKey": "0xc87509a1c067bbde78beb793e6fa76530b6382a4c0241e5e4a9ec0a0f44dc0d3"

0x62730609... is also the address to which the Mixer contract will transfer fees.

Copy config/config.example.yaml to config/local-dev.yaml to and modify it as such:

  • Change backend.hotWalletPrivKeyPath to the absolute path to the hotWalletPrivKey.json file you just created.

Install dependencies for the Semaphore submodule and compile its contracts:

cd semaphore/semaphorejs && \
npm i && \
npx truffle compile

Install dependencies and build the source code:

cd ../../
# if you are still in semaphore/semaphorejs/

npm i && \
npm run bootstrap && \
npm run build

In a new terminal, run Ganche:

# Assuming you are in mixer/

cd contracts && \

In another terminal, deploy the contracts:

# Assuming you are in mixer/

cd contracts && \
npm run deploy

In another terminal, run etcd:


In another terminal, run the relayer server:

# Assuming you are in mixer/

cd backend && \
npm run server

In another terminal, launch the frontend:

# Assuming you are in mixer/

cd frontend && \
npm run watch

Finally, launch a HTTP server to serve the zk-SNARK content:

# Assuming you are in mixer/

cd semaphore/semaphorejs/ && \
http-server -p 8000 --cors

You can now run the frontend at http://localhost:1234.

To automatically compile the TypeScript source code whenever you change it, first make sure that you have npm run watch running in a terminal. For instance, while you edit backend/ts/index.ts, have a terminal open at backend/ and then run npm run watch.

If you use a terminal multiplexer like tmux, your screen might now look like this:

Clockwise from top right:

  1. Ganache (
  2. Frontend (npm run watch)
  3. Deployed contracts (npm run deploy)
  4. HTTP server (http-server)
  5. Backend (npm run server)


Unit tests


In the mixer/contracts/ directory:

  1. Run npm run build if you haven't built the source already
  2. Run npm run testnet
  3. In a separate terminal: npm run test


In the mixer/contracts/ directory:

  1. Run npm run build if you haven't built the source already
  2. Run npm run testnet
  3. Run npm run deploy

In the mixer/backend/ directory:

  1. Run npm run build if you haven't built the source already
  2. Run npm run test


Docker containers

This project uses Docker to containerise its various components, and Docker Compose to orchestrate them.

To run build and run the Docker containers, first create a MIXER_SECRETS directory as a sibling of the mixer directory:

# Assuming you are in mixer/

cd .. && \

Create a file named hotWalletPrivKey.json in MIXER_SECRETS/ with the private key which will serve as the operator's hot wallet:

    "privateKey": "0x................................................................"

Change its file permissions:

chmod 400 MIXER_SECRETS/hotWalletPrivKey.json

Next, run:

NODE_ENV=docker ./scripts/ && \

This will produce the following images and containers (edited for brevity):

REPOSITORY              TAG                 SIZE
docker_mixer-frontend   latest              23.2MB
docker_mixer-backend    latest              2.09GB
mixer-base              latest              2.09GB
mixer-build             latest              3.24GB
nginx                   1.17.1-alpine       20.6MB
jumanjiman/etcd         latest              35MB
node                    11.14.0-stretch     904MB

CONTAINER ID        IMAGE                   COMMAND                  PORTS                          NAMES
............        docker_mixer-backend    "node build/index.js">3000/tcp         mixer-backend
............        docker_mixer-frontend   "/bin/sh -c 'nginx -…"   80/tcp,>8001/tcp   mixer-frontend
............        jumanjiman/etcd         "etcd --listen-clien…">2379/tcp         mixer-etcd

Note that setting NODE_ENV to docker-dev in the above command will make the frontend and backend use the config/docker-dev.yaml config file, which in turn points to the Kovan testnet.

In contrast, the local instances run via npm run watch in frontend/ and npm run server in backend respectively use config/local-dev.yaml, which uses any network at http://localhost:8545 with a chain ID of 1234.

Directory structure

  • frontend/: source code for the UI
  • contracts/: source code for mixer contracts and tests
  • semaphore/: a submodule for the Semaphore code


See the frontend documentation here.

Contributing pull requests

Each PR should contain a clear description of the feature it adds or problem it solves (the why), and walk the user through a summary of how it solves it.

Each PR should also add to the unit and/or integration tests as appropriate.