How to Create a MultiSig Wallet in Solidity

Creating a Multi-Sig Wallet in Solidity

A multi-signature (multi-sig) wallet is like a safe that needs multiple keys to open. It’s a smart contract that holds cryptocurrency and requires more than one person’s approval to make transactions. Today, we’ll delve into creating a multi-sig wallet using Hardhat, a popular Ethereum development environment. Creating a multi-sig wallet requires significant expertise in smart contract development. 

Prerequisites

1. A basic understanding of Solidity and Ethereum.
2. Node.js is installed on your machine.
3. Hardhat is installed globally using the command: npm install -g hardhat.

Setting Up Hardhat

1. Creating a New Project: Run npx hardhat in your terminal and follow the prompts to create a new project.
2. Installing Dependencies: Inside your project directory, install the necessary npm packages with:
   bash

npm install @nomiclabs/hardhat-waffle ethereum-waffle chai @nomiclabs/hardhat-ethers ethers

Writing the Multi-Sig Wallet Smart Contract

1. Create a new file called MultiSigWallet.sol in the contracts folder.
2. Paste the below code

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract MultiSigWallet {
   event Deposit(address indexed sender, uint amount, uint balance);
   event SubmitTransaction(
       address indexed owner,
       uint indexed txIndex,
       address indexed to,
       uint value,
       bytes data
   );
   event ConfirmTransaction(address indexed owner, uint indexed txIndex);
   event RevokeConfirmation(address indexed owner, uint indexed txIndex);
   event ExecuteTransaction(address indexed owner, uint indexed txIndex);

   address[] public owners;
   mapping(address => bool) public isOwner;
   uint public numConfirmationsRequired;

   struct Transaction {
       address to;
       uint value;
       bytes data;
       bool executed;
       uint numConfirmations;
   }

   // mapping from tx index => owner => bool
   mapping(uint => mapping(address => bool)) public isConfirmed;

   Transaction[] public transactions;

   modifier onlyOwner() {
       require(isOwner[msg.sender], "not owner");
       _;
   }

   modifier txExists(uint _txIndex) {
       require(_txIndex < transactions.length, "tx does not exist");
       _;
   }

   modifier notExecuted(uint _txIndex) {
       require(!transactions[_txIndex].executed, "tx already executed");
       _;
   }

   modifier notConfirmed(uint _txIndex) {
       require(!isConfirmed[_txIndex][msg.sender], "tx already confirmed");
       _;
   }

   constructor(address[] memory _owners, uint _numConfirmationsRequired) {
       require(_owners.length > 0, "owners required");
       require(
           _numConfirmationsRequired > 0 &&
               _numConfirmationsRequired <= _owners.length,
           "invalid number of required confirmations"
       );

       for (uint i = 0; i < _owners.length; i++) {
           address owner = _owners[i];

           require(owner != address(0), "invalid owner");
           require(!isOwner[owner], "owner not unique");

           isOwner[owner] = true;
           owners.push(owner);
       }

       numConfirmationsRequired = _numConfirmationsRequired;
   }

   receive() external payable {
       emit Deposit(msg.sender, msg.value, address(this).balance);
   }

   function submitTransaction(
       address _to,
       uint _value,
       bytes memory _data
   ) public onlyOwner {
       uint txIndex = transactions.length;

       transactions.push(
           Transaction({
               to: _to,
               value: _value,
               data: _data,
               executed: false,
               numConfirmations: 0
           })
       );

       emit SubmitTransaction(msg.sender, txIndex, _to, _value, _data);
   }

   function confirmTransaction(
       uint _txIndex
   ) public onlyOwner txExists(_txIndex) notExecuted(_txIndex) notConfirmed(_txIndex) {
       Transaction storage transaction = transactions[_txIndex];
       transaction.numConfirmations += 1;
       isConfirmed[_txIndex][msg.sender] = true;

       emit ConfirmTransaction(msg.sender, _txIndex);
   }

   function executeTransaction(
       uint _txIndex
   ) public onlyOwner txExists(_txIndex) notExecuted(_txIndex) {
       Transaction storage transaction = transactions[_txIndex];

       require(
           transaction.numConfirmations >= numConfirmationsRequired,
           "cannot execute tx"
       );

       transaction.executed = true;

       (bool success, ) = transaction.to.call{value: transaction.value}(
           transaction.data
       );
       require(success, "tx failed");

       emit ExecuteTransaction(msg.sender, _txIndex);
   }

   function revokeConfirmation(
       uint _txIndex
   ) public onlyOwner txExists(_txIndex) notExecuted(_txIndex) {
       Transaction storage transaction = transactions[_txIndex];

       require(isConfirmed[_txIndex][msg.sender], "tx not confirmed");

       transaction.numConfirmations -= 1;
       isConfirmed[_txIndex][msg.sender] = false;

       emit RevokeConfirmation(msg.sender, _txIndex);
   }

   function getOwners() public view returns (address[] memory) {
       return owners;
   }

   function getTransactionCount() public view returns (uint) {
       return transactions.length;
   }

   function getTransaction(
       uint _txIndex
   )
       public
       view
       returns (
           address to,
           uint value,
           bytes memory data,
           bool executed,
           uint numConfirmations
       )
   {
       Transaction storage transaction = transactions[_txIndex];

       return (
           transaction.to,
           transaction.value,
           transaction.data,
           transaction.executed,
           transaction.numConfirmations
       );
   }
}

Compiling Your Smart Contract:

• In your terminal, run npx hardhat compile.

Contract Details

Contract Setup

• Defined using pragma solidity ^0.8.20; to specify the Solidity compiler version.
• contract SecureMultiWallet { … } initiates the contract definition.

Event Definitions

• Events such as FundsDeposited, TransactionSubmitted, TransactionConfirmed, ConfirmationRevoked, and TransactionExecuted are defined to emit logs for significant actions within the contract.

State Variables

• authorizedUsers is an array to track wallet signatories.
• isAuthorized is a mapping to quickly verify if an address is authorized.
• requiredApprovals specifies the number of approvals needed to execute a transaction.
• pendingTransactions is an array to store all proposed transactions.
• hasConfirmed is a nested mapping to keep track of approvals per transaction.

Struct Definition

• PendingTransaction struct is defined to hold information about each proposed transaction.

Modifiers

• onlyAuthorized ensures the function is called by an authorized user.
• transactionExists checks if the transaction ID exists.
• notYetExecuted checks if the transaction has not been executed yet.
• notYetConfirmed checks if the transaction has not already been approved by the caller.

Constructor

• The constructor initializes the contract with a list of authorized users and the required number of approvals.

Fallback Function

• The receive function allows the contract to accept ether and emits a FundsDeposited event.

Transaction Management Functions

• addTransaction: Allows an authorized user to propose a new transaction.
• approveTransaction: Allows an authorized user to approve a proposed transaction.
• runTransaction: Allows an authorized user to execute a transaction once the required number of approvals have been met.
• retractApproval: Allows an authorized user to retract their approval from a proposed transaction.

View Functions

• listUsers: Allows anyone to query the list of authorized users.
• countTransactions: Allows anyone to query the total number of proposed transactions.
• fetchTransaction: Allows anyone to query details of a specific transaction by its ID.

Github: https://github.com/AshishG2/MultiSigSolidity

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