Attestable

Manages attesters and signature verification for CCTP messages

The Attestable contract provides attester management and signature verification functionality for Cross-Chain Transfer Protocol messages. It implements an m-of-n multisig mechanism where m attesters must sign messages for them to be considered valid.

Contract: src/roles/Attestable.sol

Key Concepts

• Attesters: Authorized signers who can attest to message validity
• Signature Threshold: Minimum number of signatures required (m in m/n multisig)
• Attester Manager: Role responsible for managing attesters and threshold

State Variables

signatureThreshold

uint256 public signatureThreshold

Number of signatures from distinct attesters required for a message to be received (m in m/n multisig).

enabledAttesters

EnumerableSet.AddressSet private enabledAttesters

Set of enabled attesters (message signers). The length represents n in m/n multisig.

Functions

enableAttester

function enableAttester(address newAttester) public onlyAttesterManager

Enables an attester to sign messages.

Parameters:

• newAttester: Address of the attester to enable

Requirements:

• Caller must be the attester manager
• New attester must be non-zero address
• Attester must not already be enabled

Emits: AttesterEnabled(address indexed attester)

Source: Attestable.sol:100

disableAttester

function disableAttester(address attester) external onlyAttesterManager

Disables an attester from signing messages.

Parameters:

• attester: Address of the attester to disable

Requirements:

• Caller must be the attester manager
• Must have more than one enabled attester
• Number of enabled attesters must exceed signature threshold
• Attester must currently be enabled

Emits: AttesterDisabled(address indexed attester)

Source: Attestable.sol:138

setSignatureThreshold

function setSignatureThreshold(uint256 newSignatureThreshold) external onlyAttesterManager

Updates the threshold of signatures required to attest to a message (m in m/n multisig).

Parameters:

• newSignatureThreshold: New signature threshold value

Requirements:

• Caller must be the attester manager
• New threshold must be non-zero
• New threshold must not exceed number of enabled attesters
• New threshold must be different from current threshold

Emits: SignatureThresholdUpdated(uint256 oldSignatureThreshold, uint256 newSignatureThreshold)

Source: Attestable.sol:161

updateAttesterManager

function updateAttesterManager(address newAttesterManager) external onlyOwner

Transfers attester manager control to a new address.

Parameters:

• newAttesterManager: Address of the new attester manager

Requirements:

• Caller must be the owner
• New attester manager must be non-zero address

Emits: AttesterManagerUpdated(address indexed previousAttesterManager, address indexed newAttesterManager)

Source: Attestable.sol:125

isEnabledAttester

function isEnabledAttester(address attester) public view returns (bool)

Checks if an address is an enabled attester.

Parameters:

• attester: Address to check

Returns: true if the address is an enabled attester, false otherwise

Source: Attestable.sol:109

getNumEnabledAttesters

function getNumEnabledAttesters() public view returns (uint256)

Returns the number of enabled attesters.

Returns: Count of enabled attesters

Source: Attestable.sol:117

getEnabledAttester

function getEnabledAttester(uint256 index) external view returns (address)

Gets the enabled attester at a specific index.

Parameters:

• index: Index of the attester in the set

Returns: Address of the attester at the given index

Source: Attestable.sol:180

attesterManager

function attesterManager() external view returns (address)

Returns the address of the current attester manager.

Returns: Attester manager address

Source: Attestable.sol:171

Signature Verification

Internal Verification

The contract includes internal signature verification logic:

function _verifyAttestationSignatures(
    bytes calldata _message,
    bytes calldata _attestation
) internal view

Verifies that an attestation is valid according to these rules:

1. Attestation length must equal signatureLength * signatureThreshold (65 bytes per signature)
2. Recovered addresses must be in increasing order (prevents duplicates)
3. All signers must be enabled attesters
4. Uses ECDSA signature recovery

Source: Attestable.sol:227

Modifiers

onlyAttesterManager

modifier onlyAttesterManager()

Restricts function access to the attester manager only.

Reverts: “Caller not attester manager” if caller is not the attester manager

Source: Attestable.sol:77

Events

AttesterEnabled

event AttesterEnabled(address indexed attester)

Emitted when an attester is enabled.

AttesterDisabled

event AttesterDisabled(address indexed attester)

Emitted when an attester is disabled.

SignatureThresholdUpdated

event SignatureThresholdUpdated(
    uint256 oldSignatureThreshold,
    uint256 newSignatureThreshold
)

Emitted when the signature threshold is updated.

AttesterManagerUpdated

event AttesterManagerUpdated(
    address indexed previousAttesterManager,
    address indexed newAttesterManager
)

Emitted when the attester manager is updated.

Usage Example

// Enable a new attester (as attester manager)
attestable.enableAttester(0x123...);

// Update signature threshold to require 2 signatures
attestable.setSignatureThreshold(2);

// Check if an address is an enabled attester
bool isEnabled = attestable.isEnabledAttester(0x123...);

// Get total number of attesters
uint256 count = attestable.getNumEnabledAttesters();

Security Considerations

• The signature threshold must always be less than or equal to the number of enabled attesters
• Cannot disable attesters if it would reduce the count below the threshold
• Must maintain at least one enabled attester at all times
• Signatures must be provided in ascending order by signer address to prevent duplicates
• Uses ECDSA signature recovery from OpenZeppelin for security