EVM Smart Contracts

The EVM smart contracts are deployed on the EVM networks integrated into the NoM Multi-chain Infrastructure.

Contract Anatomy

The code is written in Solidity v0.8.19 (latest as March 2023).

Imports

The smart contract uses the following openzeppelin standard contracts:

import "@openzeppelin/contracts/utils/Context.sol";
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import "@openzeppelin/contracts/utils/cryptography/ECDSA.sol";

using ECDSA for bytes32 - used to add the recover ECDSA signature functionality
using SafeERC20 for IERC20 - used to add the safeTransfer and safeTransferFrom functionalities
contract Bridge is Context - inherit _msgSender() method to get the sender

Modifiers

onlyAdministrator can only be called by owner of the administrator private key
isNotHalted can only be called if the bridge is not halted

Structs

TokenInfo is used to store information about the bridged tokens
RedeemInfo is used for redeeming funds and information regarding time challenges

Events

event RegisteredRedeem(uint256 indexed nonce, address indexed to, address indexed token, uint256 amount);
event Redeemed(uint256 indexed nonce, address indexed to, address indexed token, uint256 amount);
event Unwrapped(address indexed from, address indexed token, string to, uint256 amount);
event Halted();
event Unhalted();
event RevokedRedeem(uint256 indexed nonce);
event PendingAdministrator(address indexed newAdministrator);
event SetAdministrator(address indexed newAdministrator, address oldAdministrator);
event PendingTss(address indexed newTss);
event SetTss(address indexed newTss, address oldTss);
event PendingGuardians();
event SetGuardians();

RegisteredRedeem emitted when a redeem request is registered
Redeemed emitted when a redeem is completed
Unwrapped emitted when an unwrap request is registered
Halted emitted when the bridge is halted
Unhalted emitted when the bridge is unhalted
RevokedRedeem emitted when the administrator revokes an invalid redeem
PendingAdministrator emitted when a request for changing the administrator address is made
SetAdministrator emitted when the administrator address is set
PendingTss emitted when a request for changing the tss address is made
SetTss emitted when the tss address is set
PendingGuardians emitted when a request for changing the guardian addresses is made
SetGuardians emitted when the addresses of the guardians are set

Constants

uint256 constant uint256max stores type(uint256).max
uint32 private constant networkClass for EVM networks is hard coded to 2
uint8 private constant minNominatedGuardians must coincide with the MinGuardians constant from the embedded contract and is hard coded to 5

Variables

estimatedBlockTime is set for each network depending on the block time interval; it is used by the orchestrator to know how much to wait for one confirmation
confirmationsToFinality is the number of confirmations required to achieve finality for a given network; it is used by the orchestrator to confirm an event
halted indicates if the bridge is halted or not
allowKeyGen indicates wether or not the tss address can be changed with a valid signature; the admin can always change the tss address
administrator is the EVM compatible address of the admin
administratorDelay is the delay required for changing the admin; it cannot be lower than minAdministratorDelay
minAdministratorDelay is the minimum delay required for changing the admin
tss is the TSS address jointly created during the key generation ceremony
softDelay is the delay required for the time challenge security primitive; it cannot be lower than minSoftDelay
minSoftDelay is the minimum delay required for the time challenge security primitive
guardians is the array containing the addresses of the guardians
nominatedGuardians is the array containing the addresses of the nominated guardians
guardiansVotes is the array containing the votes for the guardians
votesCount is a mapping containing the proposed admin votes of each guardian
unhaltedAt is the last block height at which the bridge was unhalted
unhaltDuration is the duration in blocks during which the bridge is still halted after the unhaltedAt block height; it cannot be lower than minUnhaltDuration
minUnhaltDuration is the minimum duration in blocks during which the bridge is still halted after the unhaltedAt block height
actionsNonce is the nonce required for a valid signature at a particular state of the bridge; must be always incremented after a signature is validated
contractDeploymentHeight is the block height at which the contract was deployed; it is used by the orchestrator to know the height to scan events

Contract implementation

`Constructor`

In the constructor we set the following variables:

administrator
minUnhaltDuration
unhaltDuration
minAdministratorDelay
administratorDelay
minSoftDelay
softDelay
guardians
guardiansVotes
estimatedBlockTime
confirmationsToFinality
contractDeploymentHeight

The first and the second step of the redeem process. During the first step a time challenge will start. During the second step, after softDelay, the funds will be released/minted. The bridge must not be halted, the request must not have been revoked before, the token should be redeemable and the TSS signature valid.

Network of Momentum Multi-chain Infrastructure