1. Introduction

Brief explanation of the tutorial's goal

This tutorial aims to provide a comprehensive understanding of hash functions and how to implement them in a web development context. We will focus on securing passwords using hash functions, transforming them into unrecognizable strings.

What the user will learn

By the end of this tutorial, you will be able to understand what hash functions are, their importance in securing data, and have the knowledge to implement them in your own applications.

Prerequisites

Basic knowledge of web development languages (HTML, CSS, JavaScript) and Node.js is recommended. Familiarity with cryptography concepts would be beneficial, but not necessary.

2. Step-by-Step Guide

Detailed explanation of concepts

A hash function is a special type of function used in computing to map data of any size to a fixed size. In the context of passwords, it turns a plain-text password into a unique piece of 'hashed' data.

The beauty of a hash function is that the output (the hash) changes significantly with even a small change in input. This makes it practically impossible to reverse-engineer the original input from the hash, making hash functions extremely useful for storing sensitive data such as passwords.

Clear examples with comments

For example, let's consider a simple hash function that adds up the ASCII values of characters in a string. If we change even one character in the string, the sum will change, thus altering the hash.

Best practices and tips

• Always use a salt (random data) when hashing passwords. This prevents attacks using precomputed tables of hashes (rainbow table attacks).
• Do not write your own hash functions for sensitive data. Use tried and tested libraries and functions.

3. Code Examples

Example 1: Hashing a password using Node.js's crypto module

Here's a simple example of how to hash a password using Node.js's built-in 'crypto' module.

const crypto = require('crypto');

// Function to hash a password
function hashPassword(password) {
    // Creating a unique salt for a particular user
    const salt = crypto.randomBytes(16).toString('hex');

    // Hashing user's salt and password with 1000 iterations,
    // 64 length and sha512 digest
    const hash = crypto.pbkdf2Sync(password, salt,  
    1000, 64, `sha512`).toString(`hex`); 

    return [salt, hash].join('$');
}

console.log(hashPassword('mypassword'));

In this code, crypto.pbkdf2Sync is the function used to hash the password. It takes in the password, salt, number of iterations, output length, and the hashing algorithm as parameters.

Expected output

The output will be a string of characters which is the hashed password.

4. Summary

Key points covered

• What hash functions are and how they work
• How to hash passwords using a hash function
• Best practices when using hash functions

Next steps for learning

Understand different hashing algorithms and their strengths and weaknesses. Explore how to use these hash functions in a full-fledged application.

Additional resources

• Node.js Crypto Documentation: https://nodejs.org/api/crypto.html
• OWASP Password Storage Cheat Sheet: https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html

5. Practice Exercises

Exercise 1

Try implementing a hash function using a different hashing algorithm available in Node.js's crypto module.

Exercise 2

Create a small application where users can register and log in, with their passwords being hashed and stored securely.

Solutions

1. You can refer to the Node.js Crypto module documentation for a list of supported hashing algorithms.
2. The registration process should involve hashing the user's password and storing the hash (and salt) in the database. The login process should involve hashing the entered password with the stored salt and comparing it with the stored hash.

Tips for further practice

Try implementing different hash functions and comparing their outputs. Understand the importance of using a salt with hash functions.