privacy-scaling-explorations / mixer

MicroMix: A noncustodial Ethereum mixer

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

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 Implementation feature are listed here .

This mixer is highly experimental and not yet audited. Do not use it to mix real funds yet. It have been tested successfully on Ganache, Kovan ETH, Ropsten ETH, Arbitrum ETH. 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. By default 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 (deprecated and replaced with the generic Surrogeth agent), 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.

   • A MixerRegistry contract that can deploy Mixer and Semaphore contract

   • A ForwarderRegistryERC20 contract that is used by the Surrogeth deamon to register globaly and to get statistic on usage

   • Gas costs after the Istanbul network upgrade is currently 1.2 million per deposit and 378k to 420k per withdrawal. The gas cost for each withdrawal (before Istanbul) is 886k.

Local development and testing

These instructions have been tested with Debian 4.19 and Node v15 and v16

Local development

download sources

Clone this repository and its semaphore, libsemaphore and surrogeth submodule:

git clone https://github.com/jrastit/mixer.git
cd mixer
git submodule update --init

get the already build circuit from semaphore

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.

./scripts/downloadSnarks.sh

generate your circuit for semaphore (optional) (not needed if you have done the previous step)

install dependencies

Install dependencies for the libsemaphore submodule:

cd libsemaphore && \
npm i
# if you are still in libsemaphore
cd ../

Install dependencies for the Surrogeth submodule:

cd surrogeth/client && \
npm i
# if you are still in surrogeth
cd ../../

cd surrogeth/surrogethd && \
npm i
# if you are still in surrogeth
cd ../../

If you want to use other network than ganache Create a file named kovanPrivateKeys.json (or a name of your choice if you modify the config) in the mixer/key directory or for more security in a location outside this repository with a private key which will serve as the operator's hot wallet.

You can copy it from /mixer/key/ganachePrivateKey.json Don't use any of this key in production Only the first 3 values are used for testing

[
    "0xaa3680d5d48a8283413f7a108367c7299ca73f553735860a87b08f39395618b7",
    "0x0f62d96d6675f32685bbdb8ac13cda7c23436f63efbb9d07700d8669ff12b7c4",
    "0x8d5366123cb560bb606379f90a0bfd4769eecc0557f1b362dcae9012b548b1e5"
]

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

• Change key/kovanPrivateKeys.json to the absolute path to the kovanPrivateKeys.json file you just created if not in the contracts directory.

• If you want to test only on ganache, put disalbe : true on all other network (kovan, ... ) Or if you want to run the test, in config : ln -s local-test.yaml local-dev.yaml

Build the source code:

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

Run ganache for local test

Run ganache with screen

# Assuming you are in mixer/
npm run screen-ganache

Or run it in a new terminal to see the output (let it run and open a new terminal)

# Assuming you are in mixer/
npm run ganache

Clean contract deployed cache (if already deployed before with ganache):

# Assuming you are in mixer/
npm run clean-cache

Deploy the contracts if needed

Deploy the contracts:

# Assuming you are in mixer/
npm run deploy

Surrogeth

Config surrogeth from deployed contracts

Autoconfig surrogeth

# Assuming you are in mixer/
npm run surrogeth-info

Run the surrogeth with screen

# Assuming you are in mixer/
npm run screen-surrogeth

Or in another terminal, run surrogeth:

# Assuming you are in mixer/
npm run surrogeth

Run semaphore for enabling circuit download

Run semaphore server with screen

# Assuming you are in mixer/
npm run screen-semaphore

Or in annother terminal launch a HTTP server to serve the zk-SNARK content:

# Assuming you are in mixer/
npm run semahpore

Run the frontend

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

# Assuming you are in mixer/
npm run screen-frontend

in the terminal

# Assuming you are in mixer/
npm run frontend

To check the status of screen : screen -ls To check a running screen : screen -r MixerFrontend (and then to quit without killing it Ctrl + a / Ctrl + d)

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 (npm run ganache)
2. Deployed contracts (npm run deploy)
3. Frontend (npm run frontend)
4. Semaphore (npm run semaphore)
5. Surrogeth (npm run surrogeth)

Backend (Deprecated)

requirement

• etcd v3.3.13
  • The backend server requires an etcd server to lock the account nonce of its hot wallet.

Enable it in the configuration config/*.yaml

frontend:
  enableBackend: true

Run backend

Run etcd with screen

screen -S etcd -d -m etcd

Or in another terminal, run etcd:

etcd

Run the backend with screen

# Assuming you are in mixer/
npm run screen-backend

Or in another terminal, run the backend:

# Assuming you are in mixer/
npm run backend

Testing

Unit tests

Contracts

In the mixer/contracts/ directory (after starting ganache and deployed the contracts):

1. Modify the config file if needed in config/local-test.yaml you can set disable:true to disable some networks in the test
2. Run npm run screen-ganache if you are testing the ganache network
3. Run npm run clean-cache to reset contract ganache cache
4. Run npm run deploy to deploy contract
5. Run npm run surrogeth-info to configure surrogeth for testing
6. Run npm run screen-surrogeth to run surrogeth agent for testing
7. Run npm run test to run the test suite

It will run for all enabled network in config to run only specific network and token add -- --network=ganache --token=eth

Backend

In the mixer/backend/ directory (after starting ganache and deployed the contracts):

2. Run npm run test

Deployment

Docker containers

Check docker configuration file in config/docker.yaml and docker/docker-compose.yml

To build the image Run:

npm run docker-build

To run the image that will deploy the frontent on port 1235 by default http://localhost:1235/: npm run docker-start

To unload the image: npm run docker-stop

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

REPOSITORY              TAG                 SIZE
docker_mixer-frontend   latest              37.1MB
mixer-base              latest              1.44GB
mixer-build             latest              2.32GB
nginx                   1.17.1-alpine       20.6MB
node                    16-buster           20.6MB

CONTAINER ID        IMAGE                   COMMAND                  PORTS                          NAMES
............        docker_mixer-frontend   "/bin/sh -c 'nginx -…"   80/tcp, 0.0.0.0:1235->8001/tcp   mixer-frontend

In contrast, the local instances run via npm run watch in frontend/ and npm run server in backend respectively use config/local-dev.yaml.

Directory structure

• frontend/: source code for the UI
• backend/: source code for the backend deprecated and replaced with surrogeth
• contracts/: source code for mixer contracts and tests
• semaphore/: a submodule for the Semaphore code
• libsemaphore/ : a submodule for the libsemaphore
• surrogeth/ : a submodule for the Surrogeth agent

Frontend

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.

Generate your circuit for semaphore (optional)

Install Node 11.14.0 for local user to be able to run semaphore

Add at the end of ~/.profile or run it in your terminal to setup the path

export PATH=~/.npm-global/bin:$PATH
export N_PREFIX=$HOME/.npm-global

Activate change in profile:

. ~/.profile

Install npm (need any node version) you may use the one already present on the system.

wget https://nodejs.org/dist/v14.15.4/node-v14.15.4-linux-x64.tar.xz
tar -xf node-v14.15.4-linux-x64.tar.xz
export PATH=$PATH:.
cd node-v14.15.4-linux-x64/bin
npm config set prefix '~/.npm-global'

Install n (Package manager for node) and node x.x.x

npm i -g n
n x.x.x

Clean not needed version

cd ~/
rm -rf node-v14.15.4-linux-x64.tar.xz  node-v14.15.4-linux-x64

Verify

npm -v
#x.x.x

node -v
#v11.14.0

Generate the circuit

to generate the circuit in a teminal with node 11.14.0

#Check the version of node
node -v
#v11.14.0
cd semaphore/semaphorejs && \
npm i && \
cd scripts && ./build_snarks.sh
# if you are still in semaphore scripts
cd ../../../