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IMintBurnToken Interface

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Overview

• mint() is called when receiving USDC on the destination chain
• burn() is called when sending USDC from the source chain

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Interface Definition

interface IMintBurnToken is IERC20 {
    function mint(address to, uint256 amount) external returns (bool);
    function burn(uint256 amount) external;
}

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Functions

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mint

function mint(address to, uint256 amount) external returns (bool);

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Parameters

• to (address): The address that will receive the minted tokens
• amount (uint256): The amount of tokens to mint (must be less than or equal to the minter’s allowance)

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Returns

• bool: Returns true if the operation was successful

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Requirements

• Caller must have minter role
• Caller must have sufficient minter allowance
• Recipient address must not be blacklisted
• Amount must be greater than 0

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Usage in CCTP

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burn

function burn(uint256 amount) external;

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Parameters

• amount (uint256): The amount of tokens to burn from the caller’s balance

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Requirements

• Caller must have minter role
• Caller must not be blacklisted
• Amount must be less than or equal to the caller’s balance
• Amount must be greater than 0

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Usage in CCTP

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Implementation Example

contract MintBurnToken is IMintBurnToken, ERC20 {
    mapping(address => bool) public minters;
    mapping(address => uint256) public minterAllowance;
    mapping(address => bool) public blacklisted;
    
    modifier onlyMinter() {
        require(minters[msg.sender], "Caller is not a minter");
        _;
    }
    
    modifier notBlacklisted(address account) {
        require(!blacklisted[account], "Account is blacklisted");
        _;
    }
    
    function mint(address to, uint256 amount) 
        external 
        override 
        onlyMinter 
        notBlacklisted(to)
        returns (bool) 
    {
        require(amount > 0, "Amount must be greater than 0");
        require(
            amount <= minterAllowance[msg.sender],
            "Mint amount exceeds minter allowance"
        );
        
        minterAllowance[msg.sender] -= amount;
        _mint(to, amount);
        
        return true;
    }
    
    function burn(uint256 amount) 
        external 
        override 
        onlyMinter 
        notBlacklisted(msg.sender) 
    {
        require(amount > 0, "Amount must be greater than 0");
        require(amount <= balanceOf(msg.sender), "Insufficient balance");
        
        _burn(msg.sender, amount);
    }
}

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Integration with CCTP

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Token Registration

1. Implement the IMintBurnToken interface
2. Grant minter role to the TokenMinter contract
3. Set appropriate minter allowance for the TokenMinter
4. Be registered via TokenController.linkTokenPair()

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Burn-and-Mint Flow

1. Source Chain: User calls TokenMessenger.depositForBurn()
   • TokenMessenger calls TokenMinter.burn()
   • TokenMinter calls IMintBurnToken.burn() on USDC contract
   • USDC is burned from user’s balance
2. Attestation: Circle attesters sign the message hash
3. Destination Chain: Relayer calls MessageTransmitter.receiveMessage()
   • MessageTransmitter calls TokenMessenger.handleReceiveMessage()
   • TokenMessenger calls TokenMinter.mint()
   • TokenMinter calls IMintBurnToken.mint() on USDC contract
   • USDC is minted to recipient’s address

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Security Considerations

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Access Control

• Minter Role: Only authorized minters (like TokenMinter) should be able to call mint() and burn()
• Allowance Limits: Implement minter allowances to cap the maximum amount that can be minted
• Blacklisting: Support address blacklisting to comply with regulatory requirements

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Validation

• Amount Checks: Always validate that amounts are greater than zero
• Balance Checks: Ensure sufficient balance before burning
• Overflow Protection: Use SafeMath or Solidity 0.8+ to prevent overflows

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Related Interfaces

• ITokenMinter - Uses IMintBurnToken to manage token supply
• TokenMinter - Contract that calls these functions
• TokenController - Manages token pair configurations

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External Resources

• Circle USDC Implementation - Reference implementation
• ERC20 Standard - Base token standard