Password storage best practices in Flask

Introduction

Storing passwords safely protects users from hackers. It keeps their accounts and data secure.

When creating a user login system for a website or app.

When saving user passwords in a database.

When you want to prevent password theft if your database is hacked.

When you need to verify user identity securely.

When building any system that requires user authentication.

Syntax

Flask

from werkzeug.security import generate_password_hash, check_password_hash

# To store a password securely
hashed_password = generate_password_hash('user_password')

# To check a password during login
is_correct = check_password_hash(hashed_password, 'user_password')

generate_password_hash creates a safe hashed version of the password.

check_password_hash compares a stored hash with a password input.

Examples

This creates a hashed password string that looks random and safe to store.

Flask

hashed = generate_password_hash('mypassword123')
print(hashed)

This checks if the password matches the stored hash.

Flask

check_password_hash(hashed, 'mypassword123')  # returns True

This shows that a wrong password does not match the hash.

Flask

check_password_hash(hashed, 'wrongpassword')  # returns False

Sample Program

This Flask app lets users register and login. Passwords are stored safely as hashes. Login checks the password against the stored hash.

Flask

from flask import Flask, request, jsonify
from werkzeug.security import generate_password_hash, check_password_hash

app = Flask(__name__)

users = {}

@app.route('/register', methods=['POST'])
def register():
    username = request.json.get('username')
    password = request.json.get('password')
    if username in users:
        return jsonify({'message': 'User already exists'}), 400
    hashed = generate_password_hash(password)
    users[username] = hashed
    return jsonify({'message': 'User registered successfully'})

@app.route('/login', methods=['POST'])
def login():
    username = request.json.get('username')
    password = request.json.get('password')
    hashed = users.get(username)
    if not hashed or not check_password_hash(hashed, password):
        return jsonify({'message': 'Invalid username or password'}), 401
    return jsonify({'message': 'Login successful'})

# To run the app:
# flask run

# Example usage:
# POST /register with JSON {"username": "alice", "password": "secret123"}
# POST /login with JSON {"username": "alice", "password": "secret123"}

Important Notes

Never store plain text passwords. Always hash them before saving.

Use a strong hashing function like the one in Werkzeug (Flask's helper library).

Do not try to create your own hashing method; use trusted libraries.

Summary

Always hash passwords before storing them to keep user data safe.

Use generate_password_hash and check_password_hash from Werkzeug in Flask.

Never store or log plain passwords anywhere in your app.

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