Contract API

You can always get the latest version of the zkC.R.E.A.M. contract source code here.

Constructor

When you deploy the contract, you need to pass the following elements as arguments.

constructor(
    IVerifier _verifier,
    SignUpToken _signUpToken,
    uint256 _denomination,
    uint32 _merkleTreeHeight,
    address[] memory _recipients
)

Argument details

Argument	Description
`_verifier`	`Verifier` contract address. This contract can be updated later with the `updateVerifer(address)` method.
`_signUpToken`	`SignUpToken` contract address of the token to be used for voting.
`_denomination`	The total amount of tokens needed for the `deposit()` function call.
`_merkleTreeHeight`	Specify the size of the merkle tree for managing the history of deposits. The size of the tree is `2**N`.
`_recipients`	An array of ethereum addresses to be candidates for the ballot. These arrays are passed as an argument to the method `setRecipients()` when the contract is deployed, and cannot be changed after.

Deposit

The call to the deposit function is a very simple process of passing a locally generated value, in this case _commitment, but you should not forget to send the value of _denomination and have a token from the _signUpToken token contract.

function deposit (
    bytes32 _commitment
)

Argument details

Argument	Description
`_commitment`	The value of a client-generated commitment. The function `pedersenHash(nullifier, secret)` is used to generate the value of this commitment.

Usage

const instance = await Cream.deployed()
const tokenContract = await SignUpToken.deployed()

// setApprovalforall for token transfer
await tokenContract.giveToken(voter)
await tokenContract.setApprovalForAll(instance.address, true, { from: voter })

// deposit
const deposit = createDeposit(rbigInt(31), rbigInt(31))
const tx = await instance.deposit(toHex(deposit.commitment), { from: voter })
truffleAssert.eventEmitted(tx, 'Deposit')

Withdraw

function withdraw (
    bytes calldata _proof,
    bytes32 _root,
    bytes32 _nullifierHash,
    address payable _recipient,
    address payable _relayer,
    uint256 _fee
)

Argument details

Argument	Description
`_proof`	A zk-SNARK proof.
`_root`	The value of the root hash of the Merkle Tree.
`_nullifierHash`	The value of `X` of `BabyJubJub` (see here) from the return value of `nullifier` = `𝑘` passed to `pedersenHash()`.
`_recipient`	Candidate's Ethereum address. Passing an address other than the one specified in the constructor call will cause the transaction to be reverted.
`_relayer`	Relayer address.
`_fee`	Relayer fee.

Usage

// Deposit
const deposit = createDeposit(rbigInt(31), rbigInt(31))
tree.insert(deposit.commitment)
await instance.deposit(toHex(deposit.commitment), { from: voter })

// Update tree
const root = tree.root
const merkleProof = tree.getPathUpdate(0)

// Create an input
const input = {
  root,
  nullifierHash: pedersenHash(deposit.nullifier.leInt2Buff(31)).babyJubX,
  relayer: relayer,
  recipient,
  fee,
  nullifier: deposit.nullifier,
  secret: deposit.secret,
  path_elements: merkleProof[0],
  path_index: merkleProof[1]
}

let isSpent = await instance.isSpent(toHex(input.nullifierHash))
assert.isFalse(isSpent)

const {
  proof,
} = await genProofAndPublicSignals(
  input,
  'prod/vote.circom',
  'build/vote.zkey',
  'circuits/vote.wasm'
)

const args = [
  toHex(input.root),
  toHex(input.nullifierHash),
  toHex(input.recipient, 20),
  toHex(input.relayer, 20),
  toHex(input.fee)
]

const proofForSolidityInput = toSolidityInput(proof)

// Create withdraw tx
const tx = await instance.withdraw(proofForSolidityInput, ...args, { from: relayer })

truffleAssert.eventEmitted(tx, 'Withdrawal')