smashcash / heco

Smash Avax

Smash Avax is a non-custodial Ethereum and ERC20 privacy solution based on zkSNARKs. It improves transaction privacy by breaking the on-chain link between the recipient and destination addresses. It uses a smart contract that accepts ETH deposits that can be withdrawn by a different address. Whenever ETH is withdrawn by the new address, there is no way to link the withdrawal to the deposit, ensuring complete privacy.

To make a deposit user generates a secret and sends its hash (called a commitment) along with the deposit amount to the Smash smart contract. The contract accepts the deposit and adds the commitment to its list of deposits.

Later, the user decides to make a withdrawal. To do that, the user should provide a proof that he or she possesses a secret to an unspent commitment from the smart contract’s list of deposits. zkSnark technology allows that to happen without revealing which exact deposit corresponds to this secret. The smart contract will check the proof, and transfer deposited funds to the address specified for withdrawal. An external observer will be unable to determine which deposit this withdrawal came from.

You can read more about it in this medium article

Specs

• Deposit gas cost: 1088354 (43381 + 50859 * tree_depth)
• Withdraw gas cost: 301233
• Circuit Constraints = 28271 (1869 + 1325 * tree_depth)
• Circuit Proof time = 10213ms (1071 + 347 * tree_depth)
• Serverless

Requirements

1. node v11.15.0
2. npm install -g npx

Usage

You can see example usage in cli.js, it works both in the console and in the browser.

1. npm install
2. cp .env.example .env
3. npm run build - this may take 10 minutes or more
4. npx ganache-cli
5. npm run test - optionally runs tests. It may fail on the first try, just run it again.

Use browser version on Kovan:

1. vi .env - add your Kovan private key to deploy contracts
2. npm run migrate
3. npx http-server - serve current dir, you can use any other static http server
4. Open localhost:8080

Use the command-line version. Works for Ganache, Kovan, and Mainnet:

Initialization

1. cp .env.example .env
2. npm run download
3. npm run build:contract

Ganache

1. make sure you complete steps from Initialization
2. ganache-cli -i 1337
3. npm run migrate:dev
4. ./cli.js test
5. ./cli.js --help

Kovan, Mainnet

1. Please use https://github.com/smashAvax/SmartContract-BNB-ETH Example:

./cli.js deposit ETH 0.1 --rpc https://kovan.infura.io/v3/27a9649f826b4e31a83e07ae09a87448

> Relay address: 0x6A31736e7490AbE5D5676be059DFf064AB4aC754
> Getting current state from Smash contract
> Generating SNARK proof
> Proof time: 9117.051ms
> Sending withdraw transaction through the relay
> Transaction submitted through the relay. View transaction on etherscan https://kovan.etherscan.io/tx/0xcb21ae8cad723818c6bc7273e83e00c8393fcdbe74802ce5d562acad691a2a7b
> Transaction mined in block 17036120
> Done

## Deploy ETH Smash Avax

1. `cp .env.example .env`
1. Tune all necessary params
1. `npx truffle migrate --network kovan --reset --f 2 --to 4`

## Deploy ERC20 Smash Avax

1. `cp .env.example .env`
1. Tune all necessary params
1. `npx truffle migrate --network kovan --reset --f 2 --to 3`
1. `npx truffle migrate --network kovan --reset --f 5`

**Note**. If you want to reuse the same verifier for all the instances, then after you deployed one of the instances you should only run the 4th or 5th migration for ETH or ERC20 contracts respectively (`--f 4 --to 4` or `--f 5`).

## How to resolve ENS name to DNS name for a relayer

1. Visit https://etherscan.io/enslookup and put relayer ENS name to the form.
2. Copy the namehash (1) and click on the `Resolver` link (2)
   ![enslookup](docs/enslookup.png)
3. Go to the `Contract` tab. Click on `Read Contract` and scroll down to the `5. text` method.
4. Put the values:
   ![resolver](docs/resolver.png)
5. Click `Query` and you will get the DNS name. Just add `https://` to it and use it as `relayer url`

## Credits

Special thanks to @barryWhiteHat and @kobigurk for valuable input,
and @jbaylina for awesome [Circom](https://github.com/iden3/circom) & [Websnark](https://github.com/iden3/websnark) framework

## Minimal demo example

1. `npm i`
1. `ganache-cli -d`
1. `npm run download`
1. `npm run build:contract`
1. `cp .env.example .env`
1. `npm run migrate:dev`
1. `node minimal-demo.js`

## Emulate MPC trusted setup ceremony

```bash
cargo install zkutil
npx circom circuits/withdraw.circom -o build/circuits/withdraw.json
zkutil setup -c build/circuits/withdraw.json -p build/circuits/withdraw.params
zkutil export-keys -c build/circuits/withdraw.json -p build/circuits/withdraw.params -r build/circuits/withdraw_proving_key.json -v build/circuits/withdraw_verification_key.json
zkutil generate-verifier -p build/circuits/withdraw.params -v build/circuits/Verifier.sol
sed -i -e 's/pragma solidity \^0.6.0/pragma solidity 0.5.17/g' ./build/circuits/Verifier.sol