Introduction
In this Tutorial you will learn how to create a scalable and safe voting system on the Celo blockchain using solidity. We will start by emphasizing on the importance of democracy and how the blockchain technology can help to make it more transparent and secure beating fraud, theft and manipulation. After which we would go into creating the smart contract, testing, developing the smart contract and user interface as well as maintenance.
Prerequisites
To begin, you should have an understanding of the following to build a Secure and Scalable Voting System on the Celo Blockchain
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Blockchain Basics: Understanding the fundamental concepts of blockchain technology is essential. Familiarize yourself with concepts such as decentralized networks, consensus mechanisms, smart contracts, and blockchain security.
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Solidity Programming: Solidity is the programming language used for writing smart contracts on the Celo Blockchain. You should have a good understanding of Solidity syntax, data types, control structures, functions, and contract interactions.
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Celo Blockchain: Gain knowledge about the Celo Blockchain, its key features, and how it differs from other blockchain platforms. Learn about Celo’s governance protocol, native tokens (CELO and cUSD), on-chain governance, and other Celo-specific concepts.
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Celo CLI: Learn how to use the Celo Command Line Interface (CLI) to interact with the Celo Blockchain. Understand the CLI commands for deploying contracts, interacting with contracts, managing accounts, and monitoring network activity.
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Truffle Framework: Familiarize yourself with the Truffle development framework and its capabilities. Learn how to set up a development environment, compile contracts, write tests, and deploy contracts using Truffle. Understand Truffle’s configuration options and the directory structure of a Truffle project.
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Web Development: If you plan to build user interfaces for the voting system, you should have knowledge of web development technologies such as HTML, CSS, and JavaScript. Understanding web3.js, a JavaScript library for interacting with the Celo Blockchain, will be beneficial for building web-based UIs.
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Testing and Debugging: Learn how to write tests for smart contracts using Truffle’s testing framework. Understand the process of debugging smart contracts and using debugging tools provided by Truffle or other development environments.
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Deployment and Network Interaction: Gain knowledge about deploying smart contracts on the Celo Blockchain, including configuring network settings, managing gas costs, and interacting with deployed contracts using tools like the Celo Wallet, Celo CLI, or web interfaces.
Requirements
The following tools and technologies will be required to build a Cross-chain Interoperability between Celo and other Blockchain Networks.
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Celo Blockchain: The Celo Blockchain is the underlying blockchain platform used for building the voting system. It provides the infrastructure and features necessary for decentralized applications (DApps) and smart contracts.
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Solidity: Solidity is the programming language used for writing smart contracts on the Celo Blockchain. It is similar to JavaScript and specifically designed for creating DApps and executing business logic on the blockchain.
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Celo CLI: The Celo Command Line Interface (CLI) is a tool that allows developers to interact with the Celo Blockchain from the command line. It provides various commands for deploying contracts, interacting with contracts, and managing accounts on the Celo network.
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Truffle: Truffle is a popular development framework for Ethereum and Celo smart contracts. It provides a suite of tools for compiling, deploying, testing, and managing smart contracts. Truffle simplifies the development and deployment process by automating common tasks.
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Visual Studio Code: Visual Studio Code is a popular code editor that supports Solidity development. It offers various extensions and plugins specifically designed for Solidity programming, providing features such as syntax highlighting, code completion, and debugging.
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Web3.js: Web3.js is a JavaScript library that allows developers to interact with the Celo Blockchain and smart contracts. It provides an API for connecting to a Celo node, sending transactions, and calling smart contract functions from JavaScript code. Web3.js is commonly used to build web-based user interfaces for interacting with smart contracts.
Directions for Building a Secure and Scalable Voting System on the Celo Blockchain
Building a secure and scalable voting system on the Celo Blockchain using Solidity involves several steps and processes which are:
Step 1: Understand Celo Blockchain and Solidity
Understanding the Celo Blockchain: The Celo Blockchain is a decentralized platform designed to enable financial applications and services. It shares similarities with Ethereum but incorporates features specifically tailored for mobile accessibility, scalability, and stability. It utilizes a proof-of-stake consensus mechanism and supports smart contracts written in Solidity.
When building a voting system on the Celo Blockchain, you should familiarize yourself with Celo’s key concepts, such as the Celo Governance Protocol, validators, on-chain governance, and the Celo platform’s native tokens, including Celo Gold (CELO) and Celo Dollars (cUSD).
Understanding Solidity: Solidity is a high-level, statically-typed programming language used to write smart contracts on the Ethereum and Celo blockchains. It is similar to JavaScript in terms of syntax and is specifically designed for creating decentralized applications (DApps) and executing business logic on the blockchain.
Step 2: Define Voting System Logic
Define the logic of your voting system, including the rules and procedures for registration, ballot creation, voting, and tallying. Here’s an example of a simplified voting system that allows users to vote for a single candidate:
//solidity
contract VotingSystem {
struct Ballot {
string name;
uint256 voteCount;
}
struct Voter {
bool registered;
bool hasVoted;
}
mapping(address => Voter) public voters;
Ballot[] public ballots;
event VoteCasted(uint256 indexed ballotId, address indexed voter);
function registerVoter(address _voter) external {
require(!voters[_voter].registered, "Voter already registered");
voters[_voter].registered = true;
}
function createBallot(string memory _name) external {
require(voters[msg.sender].registered, "Only registered voters can create a ballot");
ballots.push(Ballot({name: _name, voteCount: 0}));
}
function castVote(uint256 _ballotId) external {
require(voters[msg.sender].registered, "Only registered voters can cast a vote");
require(!voters[msg.sender].hasVoted, "Voter has already casted a vote");
require(_ballotId < ballots.length, "Invalid ballot ID");
voters[msg.sender].hasVoted = true;
ballots[_ballotId].voteCount++;
emit VoteCasted(_ballotId, msg.sender);
}
}
Step 3: Set up Development Environment
Set up your development environment by installing the necessary tools and frameworks. You’ll need the Celo CLI and a local or testnet node to deploy and test your smart contracts.
Install Celo CLI: The Celo Command Line Interface (CLI) is a tool that allows you to interact with the Celo Blockchain from your command line. Install the Celo CLI by following the instructions provided in the Celo documentation.
Install Truffle: Choose an Integrated Development Environment (IDE): Select an IDE that supports Solidity development. In this case we’ll be using Visual Studio Code (with Solidity plugins)
Initialize a Solidity Project: run truffle init in your project directory to create the necessary configuration files and directories.
Step 4: Design Smart Contracts
This step involves defining the logic and structures that will govern the behavior of your voting system. Here are some additional considerations for designing the smart contracts:
//solidity
contract VotingSystem {
struct Ballot {
string name;
uint256[] voteCounts;
bool active;
}
struct Voter {
bool registered;
bool hasVoted;
}
mapping(address => Voter) public voters;
Ballot[] public ballots;
event VoteCasted(uint256 indexed ballotId, uint256 indexed optionId, address indexed voter);
modifier onlyRegisteredVoter() {
require(voters[msg.sender].registered, "Only registered voters can perform this action");
_;
}
modifier onlyActiveBallot(uint256 _ballotId) {
require(ballots[_ballotId].active, "The ballot is not active");
_;
}
function registerVoter(address _voter) external {
require(!voters[_voter].registered, "Voter already registered");
voters[_voter].registered = true;
}
function createBallot(string memory _name, uint256 _numOptions) external onlyRegisteredVoter {
uint256[] memory initialVoteCounts = new uint256[](_numOptions);
ballots.push(Ballot({name: _name, voteCounts: initialVoteCounts, active: true}));
}
function castVote(uint256 _ballotId, uint256 _optionId) external onlyRegisteredVoter onlyActiveBallot(_ballotId) {
require(!voters[msg.sender].hasVoted, "Voter has already casted a vote");
require(_optionId < ballots[_ballotId].voteCounts.length, "Invalid option ID");
voters[msg.sender].hasVoted = true;
ballots[_ballotId].voteCounts[_optionId]++;
emit VoteCasted(_ballotId, _optionId, msg.sender);
}
function closeBallot(uint256 _ballotId) external onlyRegisteredVoter onlyActiveBallot(_ballotId) {
ballots[_ballotId].active = false;
}
function getBallotCount() external view returns (uint256) {
return ballots.length;
}
function getOptionCount(uint256 _ballotId) external view returns (uint256) {
require(_ballotId < ballots.length, "Invalid ballot ID");
return ballots[_ballotId].voteCounts.length;
}
function getVoteCount(uint256 _ballotId, uint256 _optionId) external view returns (uint256) {
require(_ballotId < ballots.length, "Invalid ballot ID");
require(_optionId < ballots[_ballotId].voteCounts.length, "Invalid option ID");
return ballots[_ballotId].voteCounts[_optionId];
}
}
Step 5: Implement User Interfaces
Build user interfaces (UIs) that interact with the smart contracts. For web-based UIs, we can use web3.js or similar libraries to connect to the Celo Blockchain and interact with the voting system’s smart contracts. Here’s the function to cast a vote in JavaScript :
//javascript
// Import web3.js library and connect to the Celo network
const Web3 = require('web3');
const web3 = new Web3('<your-celo-provider-url>');
// Contract ABI (Application Binary Interface) - Replace with your actual ABI
const contractABI = [
// Contract functions and events
];
// Contract address - Replace with your actual contract address
const contractAddress = '<your-contract-address>';
// Instantiate the contract
const votingSystemContract = new web3.eth.Contract(contractABI, contractAddress);
// User's Celo account address
const userAddress = '<user-celo-address>';
// Function to register a voter
async function registerVoter(voterAddress) {
try {
const result = await votingSystemContract.methods.registerVoter(voterAddress).send({ from: userAddress });
console.log("Voter registered successfully:", result);
} catch (error) {
console.error("Failed to register voter:", error);
}
}
// Function to create a ballot
async function createBallot(name, numOptions) {
try {
const result = await votingSystemContract.methods.createBallot(name, numOptions).send({ from: userAddress });
console.log("Ballot created successfully:", result);
} catch (error) {
console.error("Failed to create ballot:", error);
}
}
// Function to cast a vote
async function castVote(ballotId, optionId) {
try {
const result = await votingSystemContract.methods.castVote(ballotId, optionId).send({ from: userAddress });
console.log("Vote casted successfully:", result);
} catch (error) {
console.error("Failed to cast vote:", error);
}
}
// Function to get the vote count for an option in a ballot
async function getVoteCount(ballotId, optionId) {
try {
const result = await votingSystemContract.methods.getVoteCount(ballotId, optionId).call();
console.log("Vote count:", result);
} catch (error) {
console.error("Failed to get vote count:", error);
}
}
// Example usage:
registerVoter('<voter-celo-address>');
createBallot('Presidential Election', 3);
castVote(0, 1);
getVoteCount(0, 1);
Step 6: Test and Debug
We are going to thoroughly test our smart contracts and UIs using both unit tests and integration tests using truffle
Install Truffle: We will install Truffle globally on our machine by running the following command on our terminal:
npm install -g truffle
Create Test Files: In your Truffle project directory, create a new folder called test. Inside the test folder, create JavaScript files for your unit tests, integration tests, and edge case tests. For example, you can create VotingSystem.test.js for testing the VotingSystem contract.
Write Test Cases: Open the test file (VotingSystem.test.js) and write test cases using Truffle’s testing framework. Here’s an example of a unit test for the registerVoter function:
const VotingSystem = artifacts.require("VotingSystem");
contract("VotingSystem", (accounts) => {
let votingSystemInstance;
beforeEach(async () => {
votingSystemInstance = await VotingSystem.new();
});
it("should register a voter", async () => {
const voterAddress = accounts[1];
await votingSystemInstance.registerVoter(voterAddress);
const voter = await votingSystemInstance.voters(voterAddress);
assert.equal(voter.registered, true, "Voter registration failed");
});
});
You can write additional test cases for other functions and scenarios.
Run Tests: To run the tests, execute the following command in your terminal:
truffle test
Truffle will compile the smart contracts, deploy them to a test network, and execute the defined test cases.
Debugging: If a test case fails or encounters an error, you can use Truffle’s debugging features to identify and resolve the issue.
Add console.log statements in your smart contract code to print intermediate values and debug information.
Use Truffle’s debug command to launch the debugging environment and step through the contract execution line by line.
truffle debug <transaction-hash>
Inspect the values of variables, step through the code, and identify any logical errors or inconsistencies.
Step 7: Deploy on Celo Testnet
Deploy your smart contracts on the Celo Test
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Obtain Testnet Wallet and Tokens: Create a Celo Testnet wallet and obtain test tokens (CELO and cUSD) to cover the deployment and transaction costs. You can use the Celo Wallet or other compatible wallets to access the Celo Testnet and obtain test tokens.
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Update Truffle Configuration: Open the truffle-config.js file in your Truffle project directory and update the network configuration to connect to the Celo Testnet. Add the following network configuration:
module.exports = {
// Other configuration options...
networks: {
celo_testnet: {
provider: new HDWalletProvider({
mnemonic: {
phrase: "<your-mnemonic-phrase>",
},
providerOrUrl: "<celo-testnet-provider-url>",
}),
network_id: 44787, // Celo Testnet network id
gas: 5000000, // Gas limit
gasPrice: 1000000000, // Gas price (adjust as needed)
skipDryRun: true,
},
},
};
Replace <your-mnemonic-phrase> with the mnemonic phrase of your Celo Testnet wallet and <celo-testnet-provider-url> with the URL of the Celo Testnet provider.
- Compile Contracts: In your terminal, run the following command to compile your smart contracts:
truffle compile
Truffle will compile your Solidity smart contracts and generate the contract artifacts.
Deploy Contracts: To deploy your smart contracts to the Celo Testnet, execute the following command:
truffle migrate --network celo_testnet
Truffle will deploy your contracts to the Celo Testnet using the specified network configuration. It will output the contract addresses and transaction details.
- Interact with Deployed Contract: Once your contract is deployed, you can use the contract’s address to interact with it. You can use the Celo Wallet, Celo command-line tools, or web interfaces to interact with the deployed voting system smart contract on the Celo Testnet.
Conclusion
This tutorial has taught us how to Build a Cross-chain Interoperability between Celo and other Blockchain Networks. First step was setting up a development environment, next was explaining cross-chain bridges, then developing the smart contract, deploying the smart contract and connecting to other blockchains.
Source code for project here
About the Author
Ernest Nnamdi is a Web3, Solidity, Python developer and content creator with over 5 years of experience in the tech industry. He has always been fascinated by emerging technologies and have a strong passion for blockchain and its potential to change the world.
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