Consensus - Mellow

Purpose

The Consensus contract manages a permissioned set of signers and enforces multi-signature validation logic using either EIP-712 or EIP-1271 signatures. It is a lightweight module designed for verifying offchain consensus before executing critical actions such as deposit and redemptions via SignatureQueues. It supports:

Threshold-based consensus
Two signature modes: EIP712 (EOA) and EIP1271 (contract-based)
Dynamic signer set management
Stateless, reusable verification interface

Core Concepts

Threshold-Based Verification

To validate an action, a set of authorized signers must collectively submit signatures. The number of valid signatures must be greater than or equal to the configured threshold.

Signature Types

Each signer is associated with a SignatureType:

EIP712 – Used for externally owned accounts (standard ECDSA.recover)
EIP1271 – Used for contract accounts (via isValidSignature())

Storage Layout

struct ConsensusStorage {
    uint256 threshold;
    EnumerableMap.AddressToUintMap signers;
}

threshold: Minimum number of valid signatures required for verification to succeed.
signers: Mapping of signer addresses → their configured signature type.

Initialization

function initialize(bytes calldata data)

Expects abi.encode(owner) as input.
Sets the initial owner using OwnableUpgradeable.

Signature Verification

checkSignatures

function checkSignatures(bytes32 orderHash, Signature[] calldata signatures) public view returns (bool)

Returns true if:
- At least threshold signatures are present
- Each signature is:
  - From an authorized signer
  - Valid according to the signer’s configured signature type
Returns false otherwise

Signature validation behavior:

EIP712: Uses ECDSA.recover(orderHash, sig) and matches signer
EIP1271: Calls isValidSignature(orderHash, sig) on the contract

requireValidSignatures

function requireValidSignatures(bytes32 orderHash, Signature[] calldata signatures) external view

Same logic as checkSignatures, but reverts with InvalidSignatures error if validation fails

Signer Management (Owner-only)

setThreshold

function setThreshold(uint256 threshold_) external onlyOwner

Sets a new threshold
Must be > 0 and ≤ signers.length()
Emits ThresholdSet

addSigner

function addSigner(address signer, uint256 threshold_, SignatureType sigType) external onlyOwner

Adds a new signer with specified signature type
Updates threshold (as part of signer addition)
Reverts if:
- signer == address(0)
- Signer already exists
Emits SignerAdded and ThresholdSet

removeSigner

function removeSigner(address signer, uint256 threshold_) external onlyOwner

Removes signer from consensus set
Updates threshold
Reverts if signer not found
Emits SignerRemoved and ThresholdSet

View Functions

Function	Returns
`threshold()`	Current consensus threshold
`signers()`	Total number of signers
`signerAt(uint256)`	Signer address and type at index
`isSigner(address)`	Boolean indicating if address is a signer

Events

Initialized(bytes)
ThresholdSet(uint256)
SignerAdded(address signer, SignatureType)
SignerRemoved(address signer)
InvalidSignatures(bytes32 hash, Signature[] signatures) (used in revert)

Security Considerations

Only the owner (via OwnableUpgradeable) may update signer set or threshold
Signatures are stateless and externally verifiable
Replay protection (e.g., nonce checks) must be handled by upstream systems (nonces)
Signers using EIP1271 are trusted for contract logic – contracts must not be mutable without governance

​Purpose

​Core Concepts

​Threshold-Based Verification

​Signature Types

​Storage Layout

​Initialization

​Signature Verification

​checkSignatures

​requireValidSignatures

​Signer Management (Owner-only)

​setThreshold

​addSigner

​removeSigner

​View Functions

​Events

​Security Considerations