Tornado Cash is a non-custodial Ethereum and ERC20 privacy solution based on zkSNARKs. It improves transaction privacy by breaking the on-chain link between 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 It uses a smart contract that accepts ETH deposits that can be withdrawn by a different address. Whenever ETH is withdrawn by the new address, there is no way to link the withdrawal to the deposit, ensuring complete privacy.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 Tornado smart contract. The contract accepts the deposit and adds the commitment to its list of deposits.
Later, the user decides to make a withdrawal. In order 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
- Deposit gas const: 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
Tornado.cash protocols, circuits, and smart contracts were audited by a group of experts from ABDK Consulting, specializing in zero knowledge, cryptography, and smart contracts.
During the audit no critical issues were found and all outstanding issues were fixed. The results can be found here:
- Cryptographic review https://tornado.cash/Tornado_cryptographic_review.pdf
- Smart contract audit https://tornado.cash/Tornado_solidity_audit.pdf
- Zk-SNARK circuits audit https://tornado.cash/Tornado_circuit_audit.pdf
Underlying circomlib dependency is currently being audited, and the team already published most of the fixes for found issues
node v11.15.0npm install -g npx
You can see example usage in cli.js, it works both in console and in browser.
npm installcp .env.example .envnpm run build- this may take 10 minutes or morenpx ganache-clinpm run test- optionally runs tests. It may fail on the first try, just run it again.
Use browser version on Kovan:
vi .env- add your Kovan private key to deploy contractsnpm run migratenpx http-server- serve current dir, you can use any other static http server- Open
localhost:8080
Use with command line version with Ganache:
npm run migrate:dev./cli.js deposit./cli.js withdraw <note from previous step> <destination eth address>./cli.js balance <destination eth address>
npm run migrate:dev./cli.js depositErc20./cli.js withdrawErc20 <note from previous step> <destination eth address> <relayer eth address>./cli.js balanceErc20 <destination eth address> <relayer eth address>
If you want, you can point the app to existing tornado contracts on Mainnet or Kovan. It should work without any problems
cp .env.example .env- Tune all necessary params
npx truffle migrate --network kovan --reset --f 2 --to 4
cp .env.example .env- Tune all necessary params
npx truffle migrate --network kovan --reset --f 2 --to 3npx 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 4th or 5th migration for ETH or ERC20 contracts respectively (--f 4 --to 4 or --f 5).
Special thanks to @barryWhiteHat and @kobigurk for valuable input, and to @jbaylina for awesome Circom & Websnark framework