L2TBTC

L2TBTC

Canonical L2/sidechain token implementation. tBTC token is minted on L1 and locked there to be moved to L2/sidechain. By deploying a canonical token on each L2/sidechain, we can ensure the supply of tBTC remains sacrosanct, while enabling quick, interoperable cross-chain bridges and localizing ecosystem risk.

This contract is flexible enough to:

• Delegate minting authority to a native bridge on the chain, if present.

• Delegate minting authority to a short list of ecosystem bridges.

• Have mints and burns paused by any one of n guardians, allowing avoidance of contagion in case of a chain- or bridge-specific incident.

• Be governed and upgradeable.

The token is burnable by the token holder and supports EIP2612 permits. Token holder can authorize a transfer of their token with a signature conforming EIP712 standard instead of an on-chain transaction from their address. Anyone can submit this signature on the user's behalf by calling the permit function, paying gas fees, and possibly performing other actions in the same transaction. The governance can recover ERC20 and ERC721 tokens sent mistakenly to L2TBTC token contract.

isMinter

mapping(address => bool) isMinter

Indicates if the given address is a minter. Only minters can mint the token.

minters

address[] minters

List of all minters.

isGuardian

mapping(address => bool) isGuardian

Indicates if the given address is a guardian. Only guardians can pause token mints and burns.

guardians

address[] guardians

List of all guardians.

MinterAdded

event MinterAdded(address minter)

MinterRemoved

event MinterRemoved(address minter)

GuardianAdded

event GuardianAdded(address guardian)

GuardianRemoved

event GuardianRemoved(address guardian)

onlyMinter

modifier onlyMinter()

onlyGuardian

modifier onlyGuardian()

initialize

function initialize(string _name, string _symbol) external

Initializes the token contract.

Parameters

Name	Type	Description
_name	string	The name of the token.
_symbol	string	The symbol of the token, usually a shorter version of the name.

addMinter

function addMinter(address minter) external

Adds the address to the minters list.

Requirements:

• The caller must be the contract owner.

• minter must not be a minter address already.

Parameters

Name	Type	Description
minter	address	The address to be added as a minter.

removeMinter

function removeMinter(address minter) external

Removes the address from the minters list.

Requirements:

• The caller must be the contract owner.

• minter must be a minter address.

Parameters

Name	Type	Description
minter	address	The address to be removed from the minters list.

addGuardian

function addGuardian(address guardian) external

Adds the address to the guardians list.

Requirements:

• The caller must be the contract owner.

• guardian must not be a guardian address already.

Parameters

Name	Type	Description
guardian	address	The address to be added as a guardian.

removeGuardian

function removeGuardian(address guardian) external

Removes the address from the guardians list.

Requirements:

• The caller must be the contract owner.

• guardian must be a guardian address.

Parameters

Name	Type	Description
guardian	address	The address to be removed from the guardians list.

recoverERC20

function recoverERC20(contract IERC20Upgradeable token, address recipient, uint256 amount) external

Allows the governance of the token contract to recover any ERC20 sent mistakenly to the token contract address.

Parameters

Name	Type	Description
token	contract IERC20Upgradeable	The address of the token to be recovered.
recipient	address	The token recipient address that will receive recovered tokens.
amount	uint256	The amount to be recovered.

recoverERC721

function recoverERC721(contract IERC721Upgradeable token, address recipient, uint256 tokenId, bytes data) external

Allows the governance of the token contract to recover any ERC721 sent mistakenly to the token contract address.

Parameters

Name	Type	Description
token	contract IERC721Upgradeable	The address of the token to be recovered.
recipient	address	The token recipient address that will receive the recovered token.
tokenId	uint256	The ID of the ERC721 token to be recovered.
data	bytes

pause

function pause() external

Allows one of the guardians to pause mints and burns allowing avoidance of contagion in case of a chain- or bridge-specific incident.

Requirements:

• The caller must be a guardian.

• The contract must not be already paused.

unpause

function unpause() external

Allows the governance to unpause mints and burns previously paused by one of the guardians.

Requirements:

• The caller must be the contract owner.

• The contract must be paused.

mint

function mint(address account, uint256 amount) external

Allows one of the minters to mint amount tokens and assign them to account, increasing the total supply. Emits a Transfer event with from set to the zero address.

Requirements:

• The caller must be a minter.

• account must not be the zero address.

Parameters

Name	Type	Description
account	address	The address to receive tokens.
amount	uint256	The amount of token to be minted.

burn

function burn(uint256 amount) public

Destroys amount tokens from the caller. Emits a Transfer event with to set to the zero address.

Requirements:

• The caller must have at least amount tokens.

Parameters

Name	Type	Description
amount	uint256	The amount of token to be burned.

burnFrom

function burnFrom(address account, uint256 amount) public

Destroys amount tokens from account, deducting from the caller's allowance. Emits a Transfer event with to set to the zero address.

Requirements:

• The che caller must have allowance for accounts's tokens of at least amount.

• account must not be the zero address.

• account must have at least amount tokens.

Parameters

Name	Type	Description
account	address	The address owning tokens to be burned.
amount	uint256	The amount of token to be burned.

getMinters

function getMinters() external view returns (address[])

Allows to fetch a list of all minters.

getGuardians

function getGuardians() external view returns (address[])

Allows to fetch a list of all guardians.