The ultimate guide to building a a Celo dApp with Advanced Security Features

The ultimate guide to building a Celo dApp with Advanced Security Features, I plan to create a comprehensive guide on how to build a secure dApp on the Celo platform. The guide will cover important security concepts like encryption, multi-factor authentication, and access control, and will include code examples and demonstrations to help developers understand and implement these features in their own dApps. By the end of the guide, readers will have a solid understanding of how to build a robust and secure dApp on Celo.


In this tutorial, we’ll show you step-by-step how to build a safe dApp on Celo, with a focus on advanced security features like encryption, multi-factor authentication, and access control. We will also give code examples and demos to make it easier for you to understand and use these features in your own dApps.

By the end of this guide, you will know how to build a strong and safe dApp on Celo. So, let’s get started!


Before starting with this tutorial, it is recommended to have some prior knowledge and experience in developing blockchain-based applications and familiarity with the Celo platform.

  1. Celo Account and Tokens: You will need a Celo account to interact with the Celo blockchain. You can create a Celo account using the Celo Wallet or Celo CLI. You will also need some Celo tokens to deploy and interact with your dApp on the Celo network.

  2. Solidity and Web3.js: You should have a basic understanding of Solidity, the programming language used to write smart contracts on the Ethereum network, and Web3.js, the JavaScript library used to interact with the Celo blockchain.

If you are new to Celo development or need to refresh your knowledge on any of the above prerequisites, please refer to the official Celo documentation and related tutorials to get up to speed.


Before starting with this tutorial, you should have the following software and tools installed on your development environment:

  1. Node.js: You can download and install the latest version of Node.js from the official website.

  2. Git: You will need Git installed on your computer to clone the sample code and follow along with the tutorial.

  3. Celo Wallet Extension: Install the Celo Wallet extension for your web browser to interact with the Celo blockchain.

  4. Truffle: Truffle is a development framework for Ethereum-based applications. You will need to install Truffle globally on your development environment.

  5. Ganache: Ganache is a personal blockchain for Ethereum-based applications. You will need to install Ganache to simulate a local blockchain environment.

In addition to the above software, you should also have a basic understanding of the Solidity programming language and Web3.js library, which are used to interact with the Celo blockchain.

If you are new to any of the above requirements or need to refresh your knowledge, please refer to their official documentation and tutorials.

The tutorial will also include code snippets and demonstrations to help you follow along with the instructions.

Now that we have all the requirements, we can move on to building our secure dApp on the Celo platform.

Source Code

Getting Started

To get started, we will first set up our development environment and create a new project directory. We will then create a new Solidity contract for our dApp and write the necessary code to implement advanced security features.

Setting Up the Environment

To get started, we will create a new Celo project using the Truffle framework and connect it to the Celo network using the Celo Wallet extension.

  1. Create a new Truffle project by opening a terminal and running the following command:

    truffle init
  2. Install the required dependencies for the project:

    npm install @celo/contractkit dotenv
  3. Create a .env file in the root directory of your project and add the following environment variables:


    Replace <YOUR_PRIVATE_KEY> with the private key of the Celo account that you want to use for your project. You can generate a new private key using the Celo Wallet extension.

  4. In your project’s truffle-config.js file, add the following code to connect to the Celo network:

    const ContractKit = require('@celo/contractkit')
    const dotenv = require('dotenv')
    const kit = ContractKit.newKit(process.env.CELO_PROVIDER)
    async function main() {
      const accounts = await kit.web3.eth.getAccounts()
      console.log(`Using account: ${accounts[0]}`)

    This code sets up a new ContractKit instance using the Celo provider specified in the .env file, and then prints the first account from the connected network to the console.

  5. Connect to the Celo network by running the following command:

    truffle exec connect.js --network alfajores

    This will execute the connect.js script and connect your project to the Celo network.

Congratulations! You have now connected your Truffle project to the Celo network and are ready to start building your dApp.


Encryption is an essential component of any secure dApp. It involves converting data into a code that can only be read by authorized parties. In this section, we will cover how to implement encryption in a Celo dApp.

First, we need to install the crypto package in our project. Run the following command in your project directory:

npm install crypto

Now, let’s create a new file called encryption.js and add the following code:

const crypto = require('crypto');
const algorithm = 'aes-256-cbc';
const key = crypto.randomBytes(32);
const iv = crypto.randomBytes(16);

function encrypt(text) {
  let cipher = crypto.createCipheriv(algorithm, Buffer.from(key), iv);
  let encrypted = cipher.update(text);
  encrypted = Buffer.concat([encrypted,]);
  return { iv: iv.toString('hex'), encryptedData: encrypted.toString('hex') };

function decrypt(text) {
  let iv = Buffer.from(text.iv, 'hex');
  let encryptedText = Buffer.from(text.encryptedData, 'hex');
  let decipher = crypto.createDecipheriv(algorithm, Buffer.from(key), iv);
  let decrypted = decipher.update(encryptedText);
  decrypted = Buffer.concat([decrypted,]);
  return decrypted.toString();

module.exports = { encrypt, decrypt };

The above code exports two functions, encrypt and decrypt, which we will use to encrypt and decrypt our data. The encrypt function takes a string as input and returns an object containing the encrypted data and the initialization vector (iv). The decrypt function takes the object returned by the encrypt function and returns the decrypted string.

Let’s now test our encryption and decryption functions. Add the following code to a new file called test.js:

const { encrypt, decrypt } = require('./encryption');

const text = 'This is a secret message!';

const encrypted = encrypt(text);
console.log('Encrypted:', encrypted);

const decrypted = decrypt(encrypted);
console.log('Decrypted:', decrypted);

Save the file and run it using the command node test.js. You should see the following output:

Encrypted: {
  iv: '...',
  encryptedData: '...'
Decrypted: This is a secret message!

Congratulations, you have successfully implemented encryption in your Celo dApp! Remember to keep the encryption key secure, as anyone with access to the key can decrypt the encrypted data.

Multi-Factor Authentication

Multi-Factor Authentication (MFA) is an additional layer of security that requires users to provide more than one form of authentication before being granted access to a system. The goal is to make it more difficult for an attacker to gain access to a user’s account, even if they have obtained the user’s password.

In a dApp, MFA can be implemented using different methods. One common method is to require the user to enter a One-Time Password (OTP) in addition to their password. The OTP can be generated using an authenticator app like Google Authenticator, or sent via SMS to the user’s registered phone number.

To implement MFA in your Celo dApp, you can use a library like Speakeasy to generate and verify OTPs.

Here’s an example of how you can use Speakeasy to generate an OTP for a user:

const speakeasy = require('speakeasy');

// Generate a secret for the user
const secret = speakeasy.generateSecret({length: 20});

// Save the secret to your database for later verification
const userSecret = secret.base32;

// Generate an OTP for the user
const otp = speakeasy.totp({
  secret: userSecret,
  encoding: 'base32'

console.log('User OTP:', otp);

In this example, we first generate a secret for the user using the generateSecret function. We then save the secret to our database for later verification. Finally, we generate an OTP for the user using the totp function.

To verify the OTP provided by the user, you can use the verify function provided by Speakeasy. Here’s an example:

const speakeasy = require('speakeasy');

// Verify the OTP provided by the user
const verified = speakeasy.totp.verify({
  secret: userSecret,
  encoding: 'base32',
  token: userOTP,
  window: 1 // Allow a time skew of 1 30-second interval

if (verified) {
  console.log('User authenticated successfully!');
} else {
  console.log('Invalid OTP provided');

In this example, we use the verify function to verify the OTP provided by the user. We pass in the user’s secret, the encoding used to generate the secret, the OTP provided by the user, and the window parameter, which allows for a time skew in case the user’s clock is not perfectly synchronized with the server’s clock.

Access Control

Access control is another essential security feature for dApps. It involves controlling access to specific features or data within the application based on the user’s role or permission level. By implementing access control, developers can restrict unauthorized access to sensitive information or functionality.

In Celo, access control can be achieved through the use of smart contracts. We can create a smart contract that defines different roles and permissions, and then restrict access to certain functions or data based on those roles.

Let’s consider an example of implementing access control for a simple dApp that allows users to create and edit notes. In this example, we want to restrict editing of notes to the user who created them. We will create a smart contract that defines two roles: “owner” and “editor”. Only the owner of a note can edit it, and only editors can create new notes.

// NoteAccessControl.sol

pragma solidity ^0.8.0;

contract NoteAccessControl {
    address public owner;
    mapping(address => bool) public editors;

    constructor() {
        owner = msg.sender;
        editors[owner] = true;

    modifier onlyOwner() {
        require(msg.sender == owner, "Only the owner can perform this action");

    modifier onlyEditor() {
        require(editors[msg.sender] == true, "Only editors can perform this action");

    function addEditor(address newEditor) public onlyOwner {
        editors[newEditor] = true;

    function removeEditor(address editor) public onlyOwner {
        editors[editor] = false;

    function isEditor(address user) public view returns (bool) {
        return editors[user];

In this smart contract, we define two roles: “owner” and “editor”. The owner is set to the address of the person who deploys the contract. We also define a mapping of addresses to boolean values, which will store the list of editors.

The onlyOwner modifier ensures that only the owner can perform certain actions, while the onlyEditor modifier ensures that only editors can perform other actions.

The addEditor and removeEditor functions allow the owner to add or remove editors from the list. Finally, the isEditor function allows other contracts or the dApp UI to check if a particular address is an editor.

Now let’s use this smart contract in our dApp to control access to the note editing functionality:

// Notes.sol

pragma solidity ^0.8.0;

import "./NoteAccessControl.sol";

contract Notes is NoteAccessControl {
    struct Note {
        string text;
        address owner;

    Note[] public notes;

    function create(string memory text) public onlyEditor {
        Note memory newNote = Note({
            text: text,
            owner: msg.sender

    function edit(uint256 noteIndex, string memory newText) public {
        require(notes[noteIndex].owner == msg.sender, "Only the owner can edit this note");
        notes[noteIndex].text = newText;

In this dApp smart contract, we inherit from the NoteAccessControl contract, which allows us to use the onlyEditor modifier to restrict access to the create function. We also use the onlyOwner modifier in the addEditor and removeEditor functions.

In the edit function, we use the require statement to ensure that only the owner of a note can edit it. If the caller is not the owner, the transaction will be reverted with an error message.

By using this access control scheme, we ensure that only authorized users can create and edit.


In this tutorial, we covered important security concepts like encryption, multi-factor authentication, and access control. We also provided code examples and demonstrations to help you understand and implement these features in your own dApps. By now, you should have a solid understanding of how to build a robust and secure dApp on Celo. Keep building and exploring the possibilities of blockchain technology!

Next Steps

Now that you’ve completed this tutorial, here are some next steps you can take to continue learning about building dApps on Celo:

  1. Experiment with other security features: Try implementing other security features like rate limiting, IP blocking, and OAuth2 authentication to further secure your dApp.

  2. Join the Celo community: Engage with the Celo community by joining their Discord channel and attending meetups to connect with other developers and learn from their experiences.

  3. Build your own dApp: Apply what you’ve learned from this tutorial to build your own dApp on Celo and deploy it on the testnet or mainnet.

  4. Read more about blockchain and dApp development: Stay up-to-date with the latest trends and developments in blockchain and dApp development by reading articles and tutorials on platforms like Medium and Hacker Noon.

  5. Try advanced tutorials: Check out our other tutorials on Celo and blockchain development to learn more advanced topics like smart contract development and decentralized finance (DeFi) on Celo.

About the Author

Idera Moses Oke is a technical writer with a passion for Bitcoin and cryptocurrency technology; you can find me on Twitter


Truffle documentation


I’ll be reviewing this

Great article.
However there are some mistakes in the text.
In the introduction section, there is an unwanted quotation mark.
Next steps after conclusion is not put in a proper header. Apart from that looks good

1 Like

@danielogbuti I have done the required changes, please check and approve


Looks good. You can move to publish

@danielogbuti can you tell me after reading this were you being able to understand the topic and code? Is it actually relevant information. Because for me its doesn’t look like its good content.

1 Like

The way I looked at it, he introduced specific security features with code examples. That’s what I understood it by! @Kunaldawar.

1 Like

@Kunaldawar Please can you give more insights on the areas you think I need to improve on?

1 Like

@IderaValerie The article is introductory with examples, but can you make a dapp and can you explain it in a way that your dApp incorporates this advance security features


And also add something like why we need security and how one can use it.

Thank You


Thank you @IderaValerie for the notes on Encryption and decryption. However, I sent you a suggestion in your dm.