> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/circlefin/evm-cctp-contracts/llms.txt
> Use this file to discover all available pages before exploring further.

# Pausable

> Emergency stop mechanism for CCTP contracts

The `Pausable` contract provides an emergency stop mechanism that allows authorized pausers to halt contract operations when necessary. This is a critical security feature for responding to vulnerabilities or attacks.

**Contract:** `src/roles/Pausable.sol`

## Key Concepts

* **Paused State**: Boolean flag indicating whether the contract is paused
* **Pauser Role**: Authorized address that can pause and unpause the contract
* **whenNotPaused Modifier**: Guards functions to prevent execution when paused

## State Variables

### paused

```solidity theme={null}
bool public paused = false
```

Indicates whether the contract is currently paused. When `true`, functions with the `whenNotPaused` modifier cannot be executed.

**Default:** `false`

## Functions

### pause

```solidity theme={null}
function pause() external onlyPauser
```

Pauses the contract, preventing execution of functions protected by the `whenNotPaused` modifier.

**Requirements:**

* Caller must be the pauser

**Effects:**

* Sets `paused` to `true`

**Emits:** `Pause()`

**Source:** [Pausable.sol:64](https://github.com/circlefin/evm-cctp-contracts/blob/master/src/roles/Pausable.sol#L64)

### unpause

```solidity theme={null}
function unpause() external onlyPauser
```

Unpauses the contract, restoring normal operation.

**Requirements:**

* Caller must be the pauser

**Effects:**

* Sets `paused` to `false`

**Emits:** `Unpause()`

**Source:** [Pausable.sol:72](https://github.com/circlefin/evm-cctp-contracts/blob/master/src/roles/Pausable.sol#L72)

### updatePauser

```solidity theme={null}
function updatePauser(address _newPauser) external onlyOwner
```

Updates the pauser role to a new address.

**Parameters:**

* `_newPauser`: Address of the new pauser

**Requirements:**

* Caller must be the owner
* New pauser must be non-zero address

**Emits:** `PauserChanged(address indexed newAddress)`

**Source:** [Pausable.sol:80](https://github.com/circlefin/evm-cctp-contracts/blob/master/src/roles/Pausable.sol#L80)

### pauser

```solidity theme={null}
function pauser() external view returns (address)
```

Returns the current pauser address.

**Returns:** Address of the current pauser

**Source:** [Pausable.sol:57](https://github.com/circlefin/evm-cctp-contracts/blob/master/src/roles/Pausable.sol#L57)

## Modifiers

### whenNotPaused

```solidity theme={null}
modifier whenNotPaused()
```

Restricts function execution to when the contract is not paused.

**Reverts:** "Pausable: paused" if the contract is currently paused

**Usage:** Apply to functions that should be disabled during emergency pause

**Source:** [Pausable.sol:40](https://github.com/circlefin/evm-cctp-contracts/blob/master/src/roles/Pausable.sol#L40)

**Example:**

```solidity theme={null}
function depositForBurn(
    uint256 amount,
    uint32 destinationDomain,
    bytes32 mintRecipient,
    address burnToken
) external whenNotPaused {
    // Function logic
}
```

### onlyPauser

```solidity theme={null}
modifier onlyPauser()
```

Restricts function access to the pauser only.

**Reverts:** "Pausable: caller is not the pauser" if caller is not the pauser

**Source:** [Pausable.sol:48](https://github.com/circlefin/evm-cctp-contracts/blob/master/src/roles/Pausable.sol#L48)

## Events

### Pause

```solidity theme={null}
event Pause()
```

Emitted when the contract is paused.

### Unpause

```solidity theme={null}
event Unpause()
```

Emitted when the contract is unpaused.

### PauserChanged

```solidity theme={null}
event PauserChanged(address indexed newAddress)
```

Emitted when the pauser role is transferred to a new address.

**Parameters:**

* `newAddress`: Address of the new pauser

## Internal Functions

### \_updatePauser

```solidity theme={null}
function _updatePauser(address _newPauser) internal
```

Internal function to update the pauser role.

**Parameters:**

* `_newPauser`: Address of the new pauser

**Requirements:**

* New pauser must be non-zero address

**Emits:** `PauserChanged(address indexed newAddress)`

**Source:** [Pausable.sol:87](https://github.com/circlefin/evm-cctp-contracts/blob/master/src/roles/Pausable.sol#L87)

## Usage Example

```solidity theme={null}
// Pause the contract in case of emergency (as pauser)
pausable.pause();

// Check if contract is paused
bool isPaused = pausable.paused();

// Unpause after issue is resolved
pausable.unpause();

// Transfer pauser role (as owner)
pausable.updatePauser(0x123...);
```

## Integration with CCTP

In CCTP contracts, the `whenNotPaused` modifier is applied to critical functions:

* **TokenMessenger**: `depositForBurn()`, `depositForBurnWithCaller()`, `replaceDepositForBurn()`
* **MessageTransmitter**: `receiveMessage()`, `replaceMessage()`

When paused, these operations are disabled while administrative functions remain accessible.

## Security Considerations

* The pauser role is separate from the owner role for operational flexibility
* Only the owner can change the pauser address
* Pausing is immediate and affects all protected functions
* The pauser should be a trusted address (e.g., multisig or DAO)
* Consider implementing monitoring to detect when pause is triggered
* Ensure the pauser key is highly secure and accessible during emergencies

## Origin

Forked from [Centre USDC Pausable](https://github.com/centrehq/centre-tokens/blob/0d3cab14ebd133a83fc834dbd48d0468bdf0b391/contracts/v1/Pausable.sol) with modifications:

* Updated Solidity version from 0.6.12 to 0.7.6
* Changed pauser visibility to private with external getter
* Added internal `_updatePauser` function