Password hashing with bcrypt in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of using bcrypt for password hashing?

Bcrypt securely hashes passwords to protect them from being easily read or reversed if stolen. It adds a salt and uses multiple rounds to slow down attackers.

beginner

What does the 'salt' do in bcrypt hashing?

A salt is random data added to the password before hashing. It ensures that even identical passwords have different hashes, preventing attackers from using precomputed tables.

beginner

How do you verify a password using bcrypt in Node.js?

You use bcrypt's compare function to check if the plain password matches the stored hashed password. It returns true if they match, false otherwise.

intermediate

What is the significance of the 'salt rounds' parameter in bcrypt?

Salt rounds control how many times the hashing process runs. More rounds mean stronger security but slower hashing. A common value is 10.

beginner

Show a simple example of hashing a password with bcrypt in Node.js.

```js
import bcrypt from 'bcrypt';

async function hashPassword() {
  const password = 'mySecret123';
  const saltRounds = 10;
  const hash = await bcrypt.hash(password, saltRounds);
  console.log(hash);
}

hashPassword();
``` This code creates a hashed password asynchronously.

What does bcrypt add to a password before hashing to make it more secure?

A A suffix

B A prefix

C A checksum

D A salt

Bcrypt adds a random salt to the password before hashing to ensure unique hashes.

Which bcrypt function checks if a password matches a stored hash?

A bcrypt.hash()

B bcrypt.compare()

C bcrypt.verify()

D bcrypt.check()

bcrypt.compare() compares a plain password with a hashed password.

What happens if you increase the salt rounds in bcrypt?

A Hashing becomes slower

B Hashing becomes faster

C Hashing output becomes shorter

D Hashing output becomes predictable

More salt rounds mean more hashing cycles, making hashing slower but more secure.

Why should you never store plain passwords in your database?

A They are hard to read

B They take more space

C They can be easily stolen and misused

D They slow down the app

Storing plain passwords risks user security if the database is breached.

Which of these is a valid bcrypt salt rounds value commonly used?

A 10

B 1

C 5

D 100

10 is a common default for salt rounds balancing security and performance.

Explain how bcrypt protects passwords and why it is better than simple hashing.

Think about what makes bcrypt hashes different and harder to crack.

Describe the steps to hash and verify a password using bcrypt in Node.js.

Consider both creating the hash and checking it later.

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