Smart Contracts

Dogenado's core logic is implemented in Solidity smart contracts deployed on DogeOS.

Contract Overview

Contract	Purpose
MixerPoolV2	Main pool contract for deposits/withdrawals
Verifier	Groth16 ZK proof verification
Hasher	MiMC sponge hash function

MixerPoolV2

The main mixer contract handling deposits and withdrawals.

Key Functions

deposit

function deposit(bytes32 _commitment) external

Deposits tokens into the pool:

1. Transfers tokens from user to contract
2. Inserts commitment into Merkle tree
3. Emits Deposit event

withdraw

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

Withdraws tokens from the pool:

1. Verifies the ZK proof
2. Checks nullifier hasn't been spent
3. Marks nullifier as spent
4. Transfers tokens to recipient (minus fee)

scheduleWithdrawal

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

Schedules a withdrawal with timelock:

1. Verifies the ZK proof
2. Stores withdrawal details with unlock timestamp
3. Emits WithdrawalScheduled event

executeScheduledWithdrawal

function executeScheduledWithdrawal(bytes32 _nullifierHash) external

Executes a scheduled withdrawal after timelock:

1. Checks unlock time has passed
2. Marks nullifier as spent
3. Transfers tokens to recipient

State Variables

// Immutable configuration
IVerifier public immutable verifier;
IHasher public immutable hasher;
IERC20 public immutable token;
uint256 public immutable denomination;

// Merkle tree
uint32 public constant MERKLE_TREE_HEIGHT = 20;
uint32 public currentRootIndex;
uint32 public nextIndex;
bytes32[MERKLE_TREE_HEIGHT] public filledSubtrees;
bytes32[ROOT_HISTORY_SIZE] public roots;

// Nullifier tracking
mapping(bytes32 => bool) public nullifierHashes;

// Commitment tracking
mapping(bytes32 => bool) public commitments;

// Scheduled withdrawals
mapping(bytes32 => ScheduledWithdrawal) public scheduledWithdrawals;

Events

event Deposit(
    bytes32 indexed commitment,
    uint32 leafIndex,
    uint256 timestamp
);

event Withdrawal(
    address to,
    bytes32 nullifierHash,
    address indexed relayer,
    uint256 fee
);

event WithdrawalScheduled(
    bytes32 indexed nullifierHash,
    address recipient,
    uint256 unlockTime
);

Verifier Contract

Auto-generated Groth16 verifier from the trusted setup.

Verification

function verifyProof(
    uint[2] memory a,
    uint[2][2] memory b,
    uint[2] memory c,
    uint[2] memory input
) public view returns (bool)

Inputs:

• a, b, c: Proof components
• input[0]: Root of Merkle tree
• input[1]: Nullifier hash

Returns true if the proof is valid.

Hasher Contract

Implements MiMC sponge hash for Merkle tree operations.

function MiMCSponge(
    uint256 in_xL,
    uint256 in_xR
) public pure returns (uint256 xL, uint256 xR)

Used for:

• Computing commitment hashes
• Building Merkle tree
• Computing nullifier hashes

Security Considerations

Reentrancy Protection

All external calls happen after state updates (checks-effects-interactions pattern).

Overflow Protection

Uses Solidity 0.8+ built-in overflow checks.

Access Control

• No admin functions
• No upgradability
• Immutable after deployment

Front-running Protection

• Commitments are hashed (can't predict deposits)
• Nullifiers are hashed (can't predict withdrawals)

Gas Costs

Operation	Approximate Gas
Deposit	~900,000 gas
Withdraw	~300,000 gas
Schedule Withdrawal	~350,000 gas
Execute Scheduled	~150,000 gas

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