User authentication basics in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this simple password check?

Consider this Python code snippet running on a Raspberry Pi. What will it print if the user enters the password 'raspberry'?

Raspberry Pi

password = input('Enter password: ')
if password == 'raspberry':
    print('Access granted')
else:
    print('Access denied')

A SyntaxError

B Access denied

C Access granted

D No output

💡 Hint

Check the exact string compared in the if condition.

The code compares the input to the string 'raspberry'. If they match exactly, it prints 'Access granted'. Otherwise, it prints 'Access denied'.

🧠 Conceptual

intermediate

Which method securely stores passwords on Raspberry Pi?

When building a user login system on a Raspberry Pi, which method is best to store user passwords securely?

A Store passwords hashed with a salt

B Store passwords as plain text in a file

C Store passwords encrypted with a reversible key

D Store passwords in a public shared folder

💡 Hint

Think about what makes it hard for attackers to recover the original password.

Hashing passwords with a salt means passwords are transformed into a fixed string that cannot be reversed easily. This protects passwords even if the storage is compromised.

🔧 Debug

advanced

Why does this Raspberry Pi login script always deny access?

Look at this code snippet. It should grant access if the password is 'pi123', but it always prints 'Access denied'. What is the problem?

Raspberry Pi

password = input('Enter password: ')
if password is 'pi123':
    print('Access granted')
else:
    print('Access denied')

A The print statements are reversed

B The input function is not reading the password

C The string 'pi123' is misspelled

D Using 'is' instead of '==' causes the problem

💡 Hint

Check how string comparison works in Python.

The 'is' operator checks if two variables point to the same object, not if their values are equal. For string value comparison, '==' must be used.

📝 Syntax

advanced

Identify the syntax error in this user authentication code

Which option contains the correct syntax for this Raspberry Pi Python login snippet?

Raspberry Pi

password = input('Password: ')
if password == 'secret'
    print('Welcome!')
else:
    print('Try again')

A Add a colon ':' after the if condition

B Remove the else block

C Change '==' to '=' in the if condition

D Indent the print statements less

💡 Hint

Python requires a specific punctuation after conditions.

In Python, an if statement must end with a colon ':' before the indented block.

🚀 Application

expert

How many users can this Raspberry Pi authentication dictionary hold?

Given this dictionary storing usernames and hashed passwords, how many users are registered?

Raspberry Pi

users = {
    'alice': '5f4dcc3b5aa765d61d8327deb882cf99',
    'bob': '202cb962ac59075b964b07152d234b70',
    'carol': '098f6bcd4621d373cade4e832627b4f6'
}
print(len(users))

A 2

B 3

C 0

D 4

💡 Hint

Count the number of keys in the dictionary.

The dictionary has three keys: 'alice', 'bob', and 'carol'. The len() function returns the number of keys.

Practice

1. What is the main purpose of user authentication on a Raspberry Pi?

easy

A. To speed up the Raspberry Pi's processing power

B. To verify the identity of a user before allowing access

C. To install new software automatically

D. To connect to the internet faster

Solution

1. Step 1: Understand user authentication

   User authentication is about checking who you are before access is granted.

2. Step 2: Identify the correct purpose

   Only To verify the identity of a user before allowing access describes verifying identity before access, which matches authentication.

3. Final Answer:

   To verify the identity of a user before allowing access -> Option B

4. Quick Check:

   User authentication = verify identity [OK]

Hint: Authentication means checking who you are [OK]

Common Mistakes:

• Confusing authentication with performance or internet speed
• Thinking authentication installs software
• Mixing authentication with network connection

2. Which of the following is the correct way to check a username and password in Python on Raspberry Pi?

easy

A. if username = 'pi' and password = 'raspberry':

B. if username = 'pi' or password = 'raspberry':

C. if username == 'pi' and password == 'raspberry':

D. if username == 'pi' or password == 'raspberry':

Solution

1. Step 1: Identify correct comparison operator

   In Python, '==' checks equality; '=' assigns values.

2. Step 2: Check logical operators for authentication

   Both username and password must match, so use 'and' not 'or'.

3. Final Answer:

   if username == 'pi' and password == 'raspberry': -> Option C

4. Quick Check:

   Use '==' and 'and' for correct check [OK]

Hint: Use '==' to compare and 'and' to require both true [OK]

Common Mistakes:

• Using '=' instead of '==' for comparison
• Using 'or' instead of 'and' to check both credentials
• Mixing assignment and comparison operators

3. What will be the output of this Python code on Raspberry Pi?

username = 'pi'
password = 'raspberry'
input_user = 'pi'
input_pass = 'wrongpass'

if input_user == username and input_pass == password:
    print('Access granted')
else:
    print('Access denied')

medium

A. Access granted

B. SyntaxError

C. No output

D. Access denied

Solution

1. Step 1: Compare input username and password

   input_user matches username 'pi', but input_pass is 'wrongpass', not 'raspberry'.

2. Step 2: Evaluate the if condition

   Since password check fails, condition is false, so else block runs.

3. Final Answer:

   Access denied -> Option D

4. Quick Check:

   Password mismatch means access denied [OK]

Hint: Both username and password must match exactly [OK]

Common Mistakes:

• Assuming partial match grants access
• Confusing syntax error with logic error
• Ignoring else block output

4. Find the error in this Raspberry Pi Python authentication code:

username = 'pi'
password = 'raspberry'
input_user = input('Enter username: ')
input_pass = input('Enter password: ')

if input_user = username and input_pass = password:
    print('Access granted')
else:
    print('Access denied')

medium

A. Using '=' instead of '==' in if condition

B. Missing colon ':' after if statement

C. input() function is used incorrectly

D. Print statements are missing parentheses

Solution

1. Step 1: Check the if condition syntax

   The code uses '=' which assigns values, but '==' is needed to compare values.

2. Step 2: Verify other syntax parts

   Colons are present, input() usage is correct, and print() has parentheses.

3. Final Answer:

   Using '=' instead of '==' in if condition -> Option A

4. Quick Check:

   Use '==' to compare, not '=' [OK]

Hint: Use '==' for comparison, '=' is assignment [OK]

Common Mistakes:

• Confusing assignment '=' with comparison '=='
• Forgetting colon after if statement
• Misusing input() or print() syntax

5. You want to improve a Raspberry Pi login program to lock the user out after 3 failed attempts. Which approach is best?

hard

A. Use a counter variable to track failed attempts and stop after 3

B. Change the password automatically after 3 tries

C. Print 'Access granted' even if password is wrong 3 times

D. Restart the Raspberry Pi after each failed attempt

Solution

1. Step 1: Understand the goal of locking out after 3 failures

   We need to count failed tries and stop allowing login after 3.

2. Step 2: Evaluate options for implementing this

   Using a counter variable to track attempts is the correct and simple method.

3. Final Answer:

   Use a counter variable to track failed attempts and stop after 3 -> Option A

4. Quick Check:

   Counting attempts controls login lockout [OK]

Hint: Count failed tries with a variable to limit attempts [OK]

Common Mistakes:

• Changing password automatically without user consent
• Allowing access despite wrong passwords
• Restarting device unnecessarily on failure