Password hashing with bcrypt in Node.js

Introduction

Password hashing keeps user passwords safe by turning them into secret codes that are hard to guess or reverse.

When storing user passwords in a database to protect them from theft.

When verifying a user's login password without saving the actual password.

When you want to add security to your app by making passwords unreadable.

When you need to compare a typed password with a stored hashed password.

When building any system that requires user authentication.

Syntax

Node.js

import bcrypt from 'bcrypt';

// To hash a password
const hashedPassword = await bcrypt.hash(password, saltRounds);

// To check a password
const isMatch = await bcrypt.compare(plainPassword, hashedPassword);

saltRounds controls how strong the hashing is; higher means safer but slower.

Always use await or handle promises because bcrypt functions are asynchronous.

Examples

This example hashes a password and prints the hashed result.

Node.js

const bcrypt = require('bcrypt');

const password = 'mySecret123';
const saltRounds = 10;

bcrypt.hash(password, saltRounds).then(hash => {
  console.log('Hashed password:', hash);
});

This example checks if the plain password matches the stored hashed password.

Node.js

const bcrypt = require('bcrypt');

const plainPassword = 'mySecret123';
const hashedPassword = '$2b$10$EixZaYVK1fsbw1ZfbX3OXePaWxn96p36v1bq6j6q6q6q6q6q6q6q6';

bcrypt.compare(plainPassword, hashedPassword).then(result => {
  console.log('Password match:', result);
});

Sample Program

This program hashes a password, then checks if the correct and wrong passwords match the hash, printing the results.

Node.js

import bcrypt from 'bcrypt';

async function run() {
  const password = 'helloWorld!';
  const saltRounds = 12;

  // Hash the password
  const hashed = await bcrypt.hash(password, saltRounds);
  console.log('Hashed password:', hashed);

  // Verify the password
  const isValid = await bcrypt.compare('helloWorld!', hashed);
  console.log('Password is valid:', isValid);

  const isInvalid = await bcrypt.compare('wrongPassword', hashed);
  console.log('Wrong password is valid:', isInvalid);
}

run();

Important Notes

Never store plain passwords, always store hashed versions.

Use a saltRounds value of at least 10 for good security.

Hashing is one-way: you cannot get the original password back from the hash.

Summary

Password hashing protects user data by turning passwords into secret codes.

Use bcrypt's hash to create a hashed password and compare to check passwords.

Always handle bcrypt functions asynchronously with await or promises.

Practice

1. What is the main purpose of using bcrypt in a Node.js application?

easy

A. To securely hash user passwords before storing them

B. To encrypt user data for faster retrieval

C. To compress files on the server

D. To generate random user IDs

Solution

1. Step 1: Understand bcrypt's role

   Bcrypt is designed to hash passwords securely, making them hard to reverse.

2. Step 2: Identify the correct purpose

   Encrypting data or compressing files are not bcrypt's functions; it focuses on password hashing.

3. Final Answer:

   To securely hash user passwords before storing them -> Option A

4. Quick Check:

   Password hashing = Secure storage [OK]

Hint: Bcrypt is for password security, not encryption or compression [OK]

Common Mistakes:

• Confusing hashing with encryption
• Thinking bcrypt compresses data
• Assuming bcrypt generates IDs

2. Which of the following is the correct way to hash a password asynchronously using bcrypt in Node.js?

easy

A. const hashed = await bcrypt.hash(password, 10);

B. const hashed = bcrypt.hashSync(password, 10);

C. const hashed = bcrypt.compare(password, 10);

D. const hashed = bcrypt.hash(password);

Solution

1. Step 1: Identify asynchronous hashing syntax

   Bcrypt's async hash function requires await and two arguments: password and salt rounds.

2. Step 2: Check each option

   hashSync uses the synchronous method, compare is for verification not hashing, and the hash call misses salt rounds.

3. Final Answer:

   const hashed = await bcrypt.hash(password, 10); -> Option A

4. Quick Check:

   Async hash needs await and salt rounds [OK]

Hint: Async bcrypt hash needs await and salt rounds [OK]

Common Mistakes:

• Using hashSync instead of async hash
• Calling compare instead of hash
• Omitting salt rounds argument

3. What will the following code output if the password matches the hash?

const bcrypt = require('bcrypt');

async function check() {
  const password = 'secret123';
  const hash = await bcrypt.hash(password, 10);
  const result = await bcrypt.compare('secret123', hash);
  console.log(result);
}
check();

medium

A. false

B. true

C. undefined

D. Error

Solution

1. Step 1: Understand bcrypt.compare behavior

   It returns true if the plain password matches the hashed password.

2. Step 2: Analyze the code flow

   The password 'secret123' is hashed and then compared with the same password, so result is true.

3. Final Answer:

   true -> Option B

4. Quick Check:

   Matching password returns true [OK]

Hint: Compare returns true if passwords match [OK]

Common Mistakes:

• Expecting false for matching passwords
• Confusing compare with hash
• Ignoring async/await in code

4. Identify the error in this bcrypt usage:

const bcrypt = require('bcrypt');

async function verify() {
  const password = 'mypassword';
  const hash = bcrypt.hash(password, 10);
  const match = await bcrypt.compare(password, hash);
  console.log(match);
}
verify();

medium

A. Incorrect salt rounds value

B. Using compare instead of hash to create hash

C. Password variable is not defined

D. Missing await before bcrypt.hash causing hash to be a Promise

Solution

1. Step 1: Check bcrypt.hash usage

   Bcrypt.hash is async and returns a Promise, so it needs await to get the hashed string.

2. Step 2: Identify the error impact

   Without await, hash is a Promise, causing compare to fail or behave unexpectedly.

3. Final Answer:

   Missing await before bcrypt.hash causing hash to be a Promise -> Option D

4. Quick Check:

   Async hash needs await [OK]

Hint: Always await async bcrypt.hash calls [OK]

Common Mistakes:

• Forgetting await on async functions
• Confusing compare with hash
• Using invalid salt rounds

5. You want to securely store user passwords and verify them later. Which approach correctly combines hashing and verification using bcrypt in an async function?

hard

A. Hash password synchronously with bcrypt.hashSync(password, 12) and verify asynchronously with await bcrypt.compare(input, storedHash)

B. Store the plain password and verify by hashing input with bcrypt.hashSync(input, 12) and comparing strings

C. Hash the password with await bcrypt.hash(password, 12) and verify with await bcrypt.compare(input, storedHash)

D. Encrypt password with bcrypt.encrypt(password) and decrypt for verification

Solution

1. Step 1: Choose secure async hashing and verification

   Using async bcrypt.hash with salt rounds (12) and async bcrypt.compare is best practice.

2. Step 2: Evaluate other options

   Storing plain passwords and hashing input for string comparison is insecure, mixing sync hashing with async verification is inconsistent, and bcrypt has no encrypt/decrypt methods.

3. Final Answer:

   Hash the password with await bcrypt.hash(password, 12) and verify with await bcrypt.compare(input, storedHash) -> Option C

4. Quick Check:

   Async hash and compare with salt rounds = secure [OK]

Hint: Use async hash and compare with salt rounds for security [OK]

Common Mistakes:

• Storing plain passwords
• Mixing sync and async bcrypt calls
• Assuming bcrypt can encrypt/decrypt