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Tornado cash. Non-custodial private transactions on Ethereum.
circuits | ||
contracts | ||
lib | ||
migrations | ||
test | ||
.editorconfig | ||
.env.example | ||
.eslintrc.json | ||
.gitattributes | ||
.gitignore | ||
.nvmrc | ||
.travis.yml | ||
cli.js | ||
index.html | ||
LICENSE | ||
mixer.png | ||
package-lock.json | ||
package.json | ||
README.md | ||
truffle-config.js |
Tornado mixer
Specs
- Deposit gas cost: deposit 888054
- Withdraw gas cost: 692133
- Circuit constraints: 22617
- Circuit proving time: 6116ms
- Serverless
Security risks
- Cryptographic tools used by mixer (zkSNARKS, Pedersen commitment, MiMC hash) are not yet extensively audited by cryptographic experts and may be vulnerable
- Note: we use MiMC hash only for merkle tree, so even if a preimage attack on MiMC is discovered, it will not allow to deanonymize users. To drain funds attacker needs to be able to generate arbitrary hash collisions, which is a pretty strong assumption.
- Relayer is frontrunnable. When relayer submits a transaction someone can see it in tx pool and frontrun it with higher gas price to get the fee and drain relayer funds.
- Workaround: we can set high gas price so that (almost) all fee is used on gas. The relayer will not receive profit this way, but this approach is acceptable until we develop more sophisticated system that prevents frontrunning
- Bugs in contract. Even though we have an extensive experience in smart contract security audits, we can still make mistakes. An external audit is needed to reduce probablility of bugs
Nullifier griefing. when you submit a withdraw transaction you reveal the nullifier for your note. If someone manages to make a deposit with the same nullifier and withdraw it while your transaction is still in tx pool, your note will be considered spent since it has the same nullifier and it will prevent you from withdrawing your funds- Fixed by sending nullifier hash instead of plain nullifier
Requirements
node v11.15.0
npm install -g npx
Usage
npm i
cp .env.example .env
npm run build:circuit
- may take 10 minutes or morenpm run build:contract
npm run browserify
npx ganache-cli
npm run test
- optionally run tests. It may fail for the first time, just run one more time.npm run migrate:dev
./cli.js deposit
./cli.js withdraw <note from previous step> <destination eth address>
./cli.js balance <destination eth address>
vi .env
- add your Kovan private key to deploy contractsnpm run migrate
npx http-server
- serve current dir, you can use any other http server- Open
localhost:8080
Credits
Special thanks to @barryWhiteHat and @kobigurk for valuable input, and to @jbaylina for awesome Circom & Websnark framework