atvanguard / optimistic-zkdai

An optimistic implementation of ZkDai

optimistic-zkdai

• The zkdai components are based on the latest spec.
• Learn about the ingredients behind ZkDai from ZkDai — Private DAI transactions on Ethereum using Zk-SNARKs.
• The optimistic nature of the contracts is inspired from Optimistic Contracts.

Lifecycle of a zkdai note

• To mint a zkdai note worth x Dai, dai.approve the zkdai contract to move x tokens.
• Generate a zkSnark (using zokrates) with appropriate params. See mintNoteZokcmd.js.
• Send a transaction calling zkdai.mint with the proof and send along the required stake. The contract will transfer x Dai tokens from user to itself and save the hash of the proof on-chain. The hash will be saved on-chain instead of the entire proof to save gas. The note is not yet committed.
• Before the challenge period ends, a watchful verifier can challenge the proof if the verifier notices that an invalid zkSnark was submitted. This would entail reading the submitted proof from the transaction above and sending it to zkdai.challenge. The challenged proof will then be verified. If the the challenge passes, the submitter's stake would be slashed and transferred to the the challenger; if the challenge fails, the zkdai note will be committed and the stake will be returned to the proof submitter.
• Alternatively, if the proof remained unchallenged during the challenge period, the submitter can commit the note by calling zkdai.commit.
• Similarly, to spend a zkdai note, the user would need to generate and submit the zkSnark proof to zkdai.spend. See spendNoteZokcmd.js. The challenge and commit phases will follow the same mechanism as above.
• At any point, the user can choose to liquidate a zkdai note. The user submits the zkSnark. The contract verifies the proof, marks the note as Spent and transfers the equivalent amount of Dai to the specified recepient.

Tests

ganache-cli
npm test

Development

zokrates

Run container

git clone [e-mail]:Zokrates/ZoKrates.git
cd ZoKrates
docker build -t zokrates .
docker run --name zokrates -ti zokrates /bin/bash

Setup circuit and export solidity verifier

docker cp circuits/createNote.code zokrates:/home/zokrates/

(in container)
./zokrates compile -i createNote.code
./zokrates setup
./zokrates export-verifier

docker cp zokrates:/home/zokrates/verifier.sol contracts/verifiers/MintNoteVerifier.sol

Generate witness and proof

node scripts/mintNoteZokcmd.js

(in container)
Paste the command printed above in zokrates container (computes witness)
./zokrates generate-proof

docker cp zokrates:/home/zokrates/proof.json test/mintNoteProof.json