Password storage best practices in Flask - Performance & Optimization

Performance: Password storage best practices

HIGH IMPACT

This affects server response time during user authentication and overall security of stored passwords.

Storing user passwords securely in a Flask application

Flask

from werkzeug.security import generate_password_hash

# Using strong salted hash
password_hash = generate_password_hash('user_password', method='pbkdf2:sha256', salt_length=16)

PBKDF2 with SHA-256 and salt slows hashing to prevent brute force while keeping server responsive.

📈 Performance GainBalances CPU cost with security; hashing takes ~100ms but prevents attacks.

Storing user passwords securely in a Flask application

Flask

import hashlib

# Using fast hash without salt
password_hash = hashlib.md5(b'user_password').hexdigest()

MD5 is a fast, outdated hash without salt, making it vulnerable to brute force and rainbow table attacks.

📉 Performance CostFast hashing reduces CPU time but compromises security, risking data breaches.

Performance Comparison

Pattern	CPU Usage	Blocking	Security	Verdict
Fast hash (MD5) without salt	Low	No	Very weak	[X] Bad
Plaintext password comparison	Negligible	No	None	[X] Bad
Synchronous PBKDF2 hashing	High	Yes	Strong	[!] OK
Asynchronous PBKDF2 hashing	High	No	Strong	[OK] Good

Rendering Pipeline

Password hashing runs on the server and does not affect browser rendering pipeline directly, but impacts server response time which affects user experience.

→Server CPU processing

→Network response time

⚠️ BottleneckCPU-intensive hashing can block server threads causing slower responses.

Optimization Tips

1Always use salted, slow hashing algorithms like PBKDF2, bcrypt, or Argon2.

2Avoid synchronous hashing on main server threads to prevent blocking.

3Never store or compare plaintext passwords directly.

Performance Quiz - 3 Questions

Why should you use a slow hashing algorithm like PBKDF2 for password storage?

A It reduces server CPU usage significantly.

B It makes brute force attacks slower and more difficult.

C It speeds up user login time.

D It avoids the need for salting passwords.

DevTools: Network and Performance panels

How to check: Use Network panel to measure server response time during login. Use Performance panel to check if server delays cause slow responses.

What to look for: Look for increased server response time during password hashing; long blocking times indicate synchronous hashing.

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