Two-factor authentication in Intro to Computing - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the main purpose of two-factor authentication?

Imagine you have a safe that requires two different keys to open. What is the main reason for using two keys instead of just one?

A To increase security by requiring two different proofs of identity

B To allow more people to open the safe at the same time

C To make it easier to open the safe quickly

D To reduce the cost of making keys

💡 Hint

Think about how having two locks instead of one affects safety.

Two-factor authentication requires two different types of proof to confirm identity, making unauthorized access much harder.

❓ trace

intermediate

Trace the steps in a two-factor authentication process

Follow the steps below and identify what happens after the user enters their password correctly.

1. User enters username and password.
2. System checks password.
3. ?
4. User enters code from their phone.
5. System verifies code and grants access.

A System resets the user's password.

B System asks for a security question answer.

C System logs the user out immediately.

D System sends a code to the user's phone.

💡 Hint

Think about what the second factor usually is in two-factor authentication.

After verifying the password, the system sends a code to the user's phone as the second factor.

❓ Comparison

advanced

Compare single-factor and two-factor authentication

Which of the following best explains the difference between single-factor and two-factor authentication?

A Single-factor requires only one proof of identity; two-factor requires two different proofs.

B Single-factor uses two passwords; two-factor uses one password and one code.

C Single-factor is more secure than two-factor authentication.

D Two-factor authentication does not require a password.

💡 Hint

Think about how many types of identity proof each method requires.

Single-factor authentication uses one proof (like a password), while two-factor requires two different proofs (like password + code).

❓ identification

advanced

Identify the second factor in two-factor authentication

Which of the following is commonly used as the second factor in two-factor authentication?

A Email address

B Password

C Fingerprint or code sent to phone

D Username

💡 Hint

The second factor is usually something you have or something you are.

The second factor is often a fingerprint (something you are) or a code sent to your phone (something you have).

🚀 Application

expert

What happens if the second factor code is entered incorrectly multiple times?

Consider a system that locks the user out after three wrong two-factor codes. What is the main reason for this behavior?

A To allow the user to try unlimited times without risk

B To prevent unauthorized access by blocking repeated guessing

C To reset the user's password automatically

D To send the correct code to the user again

💡 Hint

Think about how repeated wrong attempts can be a security risk.

Locking out after multiple wrong attempts stops attackers from guessing codes repeatedly.

Practice

1. What is the main purpose of two-factor authentication (2FA)?

easy

A. To allow users to log in without any password

B. To make passwords shorter and easier to remember

C. To add an extra layer of security by requiring two ways to prove identity

D. To speed up the login process by skipping verification

Solution

1. Step 1: Understand what 2FA means

   Two-factor authentication means using two different methods to confirm who you are.

2. Step 2: Identify the main goal of 2FA

   The goal is to make it harder for others to access your account by adding extra security.

3. Final Answer:

   To add an extra layer of security by requiring two ways to prove identity -> Option C

4. Quick Check:

   Extra security = To add an extra layer of security by requiring two ways to prove identity [OK]

Hint: 2FA means two ways to prove identity, not shortcuts [OK]

Common Mistakes:

• Thinking 2FA makes passwords shorter
• Believing 2FA removes the need for passwords
• Assuming 2FA speeds up login by skipping steps

2. Which of the following is a correct example of a second factor in two-factor authentication?

easy

A. A code sent to your phone via SMS

B. A password you create

C. Your username

D. Your email address

Solution

1. Step 1: Identify what counts as a second factor

   The second factor is something you have or receive, like a code sent to your phone.

2. Step 2: Compare options to the second factor definition

   A password and username are first factors; a code sent to your phone is a second factor.

3. Final Answer:

   A code sent to your phone via SMS -> Option A

4. Quick Check:

   Second factor = code on phone [OK]

Hint: Second factor is usually a code or device, not password [OK]

Common Mistakes:

• Confusing password as second factor
• Thinking username or email is a second factor
• Ignoring the difference between first and second factors

3. Consider this flowchart for a login process with two-factor authentication:

What happens if the password is correct but the code is wrong?

medium

A. Access is granted immediately

B. Access is denied after code verification fails

C. User is asked to enter the password again

D. User is logged in without code verification

Solution

1. Step 1: Follow the flowchart steps

   The user enters password first; if correct, then code is requested.

2. Step 2: Check what happens if code is wrong

   If the code verification fails, the flowchart shows access is denied.

3. Final Answer:

   Access is denied after code verification fails -> Option B

4. Quick Check:

   Wrong code = access denied [OK]

Hint: Both password and code must be correct to access [OK]

Common Mistakes:

• Assuming password alone grants access
• Thinking user retries password after code fails
• Ignoring the code verification step

4. A user complains they cannot log in even after entering the correct password and code. Which of these is a likely error in the two-factor authentication process?

medium

A. The password was too simple

B. The user entered the wrong username

C. The user did not enter any code

D. The code sent to the user expired before use

Solution

1. Step 1: Analyze the problem with correct password and code

   If the password and code are correct but login fails, the code might have expired.

2. Step 2: Eliminate other options

   Wrong username or no code would cause different errors; password simplicity does not block login.

3. Final Answer:

   The code sent to the user expired before use -> Option D

4. Quick Check:

   Expired code blocks login [OK]

Hint: Expired codes cause login failure despite correct input [OK]

Common Mistakes:

• Blaming password strength for login failure
• Ignoring code expiration time
• Assuming username error when password is correct

5. You want to improve your online account security using two-factor authentication. Which combination below is the best choice?

hard

A. Password + fingerprint scan on your phone

B. Password + security question answer

C. Password + username

D. Password + code sent by email

Solution

1. Step 1: Identify strong second factors

   Biometric methods like fingerprint scans are stronger and harder to fake than codes or questions.

2. Step 2: Compare options for security

   Code by email can be intercepted; username is not a factor; security questions can be guessed.

3. Final Answer:

   Password + fingerprint scan on your phone -> Option A

4. Quick Check:

   Biometric second factor = strongest security [OK]

Hint: Biometrics + password is stronger than codes or questions [OK]

Common Mistakes:

• Thinking username is a second factor
• Believing email codes are always safest
• Underestimating security questions' weakness