Password storage best practices in Flask - Cheat Sheet & Quick Revision

Recall & Review

beginner

Why should passwords never be stored in plain text?

Storing passwords in plain text is dangerous because if the database is hacked, attackers get direct access to user passwords. This can lead to account theft and further security breaches.

beginner

What is hashing in the context of password storage?

Hashing is a one-way process that converts a password into a fixed-length string of characters. It is designed so you cannot reverse it to get the original password, making it safer to store.

intermediate

What role does a salt play in password hashing?

A salt is a random string added to a password before hashing. It ensures that even if two users have the same password, their hashes will be different, protecting against attacks using precomputed tables.

beginner

Which Python library is recommended for secure password hashing in Flask?

The 'werkzeug.security' module is recommended in Flask. It provides functions like generate_password_hash() and check_password_hash() to safely hash and verify passwords.

intermediate

Why is using a slow hashing algorithm important for password storage?

Slow hashing algorithms make it harder for attackers to try many password guesses quickly. This reduces the risk of brute-force attacks and improves security.

Which of the following is the safest way to store passwords in a Flask app?

A Hash passwords using SHA-1 without salt

B Use werkzeug.security's generate_password_hash with salt

C Store passwords as plain text in the database

D Encrypt passwords with reversible encryption

Using werkzeug.security's generate_password_hash adds salt and uses a strong hashing algorithm, making it the safest option.

What does adding a salt to a password hash prevent?

A Rainbow table attacks

B Password length issues

C Password reuse by users

D Database connection errors

Salts prevent rainbow table attacks by making each hash unique, even for identical passwords.

Which function in Flask's Werkzeug library checks if a password matches its hash?

A verify_password()

B validate_password()

C check_password_hash()

D compare_hash()

check_password_hash() compares a stored hash with a password attempt securely.

Why should password hashing algorithms be slow?

A To make brute-force attacks slower

B To save server resources

C To speed up user login

D To reduce password length

Slow hashing algorithms increase the time needed for each guess, making brute-force attacks less practical.

What is a common hashing algorithm used by generate_password_hash in Flask?

A MD5

B SHA-256

C Base64

D PBKDF2

generate_password_hash uses PBKDF2 by default, which is a slow and secure hashing algorithm.

Explain the steps you would take to securely store user passwords in a Flask application.

Think about how to protect passwords from attackers if the database is leaked.

Describe why salting passwords is important and how it improves security.

Consider what happens if two users have the same password.

Practice

1. Why should you never store plain text passwords directly in your Flask application's database?

easy

A. Because plain text passwords can be easily stolen if the database is compromised.

B. Because plain text passwords take up more space than hashed passwords.

C. Because Flask does not support storing plain text passwords.

D. Because hashed passwords are faster to compare than plain text passwords.

Solution

1. Step 1: Understand password security risks

   Storing plain text passwords means if someone hacks the database, they get all user passwords directly.

2. Step 2: Importance of hashing

   Hashing transforms passwords into unreadable strings, protecting user data even if the database leaks.

3. Final Answer:

   Because plain text passwords can be easily stolen if the database is compromised. -> Option A

4. Quick Check:

   Password safety = Avoid plain text storage [OK]

Hint: Never store passwords as plain text, always hash first [OK]

Common Mistakes:

• Thinking hashing is optional
• Believing plain text is safe if database is secure
• Confusing hashing with encryption

2. Which of the following is the correct way to hash a password using Werkzeug in Flask?

easy

A. hashed = make_password(password)

B. hashed = generate_password_hash(password)

C. hashed = password_hash(password)

D. hashed = hash_password(password)

Solution

1. Step 1: Recall Werkzeug's hashing function

   Werkzeug provides generate_password_hash to hash passwords securely.

2. Step 2: Identify correct function usage

   The correct function call is generate_password_hash(password), other options are invalid or non-existent.

3. Final Answer:

   hashed = generate_password_hash(password) -> Option B

4. Quick Check:

   Use generate_password_hash() to hash passwords [OK]

Hint: Use generate_password_hash() from Werkzeug to hash passwords [OK]

Common Mistakes:

• Using non-existent functions like hash_password
• Confusing hashing with encryption functions
• Trying to hash passwords manually

3. What will the following Flask code output if the password check is correct?

from werkzeug.security import generate_password_hash, check_password_hash
hashed = generate_password_hash('secret123')
result = check_password_hash(hashed, 'secret123')
print(result)

medium

A. False

B. secret123

C. Error

D. True

Solution

1. Step 1: Understand generate_password_hash output

   This function creates a hashed string from 'secret123'.

2. Step 2: Check password correctness with check_password_hash

   It compares the hashed password with the plain text 'secret123' and returns True if they match.

3. Final Answer:

   True -> Option D

4. Quick Check:

   check_password_hash returns True if passwords match [OK]

Hint: check_password_hash returns True when password matches hash [OK]

Common Mistakes:

• Expecting the original password as output
• Confusing True/False return values
• Assuming check_password_hash modifies the hash

4. Identify the error in this Flask password check code:

from werkzeug.security import generate_password_hash, check_password_hash
hashed = generate_password_hash('mypassword')
if check_password_hash('mypassword', hashed):
    print('Access granted')

medium

A. The hashed and plain password arguments are reversed in check_password_hash.

B. generate_password_hash should not be used for hashing passwords.

C. The print statement should be outside the if block.

D. There is no error; the code works correctly.

Solution

1. Step 1: Check argument order in check_password_hash

   The first argument must be the hashed password, second is the plain password.

2. Step 2: Identify the reversed arguments

   The code passes plain password first and hash second, causing a logic error.

3. Final Answer:

   The hashed and plain password arguments are reversed in check_password_hash. -> Option A

4. Quick Check:

   check_password_hash(hash, password) order matters [OK]

Hint: Pass hashed first, plain password second to check_password_hash [OK]

Common Mistakes:

• Swapping arguments in check_password_hash
• Using generate_password_hash incorrectly
• Ignoring function argument order

5. You want to securely store user passwords in your Flask app and verify them on login. Which approach follows best practices?

hard

A. Store plain passwords in the database and compare them directly on login.

B. Encrypt passwords with a reversible method and decrypt them on login to compare.

C. Hash passwords with generate_password_hash before storing, then verify with check_password_hash during login.

D. Store passwords as plain text but log them only during login attempts.

Solution

1. Step 1: Understand secure password storage

   Passwords must be hashed before storing to prevent exposure if database leaks.

2. Step 2: Verify passwords securely on login

   Use check_password_hash to compare the stored hash with the login password safely.

3. Final Answer:

   Hash passwords with generate_password_hash before storing, then verify with check_password_hash during login. -> Option C

4. Quick Check:

   Hash before store, verify with check_password_hash [OK]

Hint: Hash before store, verify with check_password_hash on login [OK]

Common Mistakes:

• Storing or logging plain passwords
• Using reversible encryption instead of hashing
• Comparing plain passwords directly