User authentication mechanisms in Operating Systems - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary purpose of multi-factor authentication (MFA)?

Multi-factor authentication (MFA) is a security method used in user authentication. What is its main goal?

A To store user passwords in an encrypted file on the server

B To allow users to log in without a password by using only a fingerprint

C To require users to provide two or more different types of evidence to verify their identity

D To limit the number of login attempts before locking the account

💡 Hint

Think about how MFA increases security beyond just a password.

MFA requires users to provide multiple types of evidence, such as something they know (password), something they have (a phone), or something they are (fingerprint), making unauthorized access harder.

📋 Factual

intermediate

Which authentication method uses a secret shared between the user and the system?

Among common authentication methods, which one relies on a secret known only to the user and the system?

A Token-based authentication

B Password-based authentication

C Biometric authentication

D Certificate-based authentication

💡 Hint

Consider which method requires memorizing a secret string.

Password-based authentication uses a secret password shared only between the user and the system to verify identity.

🔍 Analysis

advanced

What error will occur if a system tries to authenticate a user with a missing biometric template?

Consider a system that uses fingerprint data stored as a biometric template. What happens if the template is missing when the user tries to authenticate?

A Authentication fails due to missing data, resulting in an error or denial

B The system automatically falls back to password authentication without error

C The system grants access because no template means no check is needed

D The system crashes with a runtime exception

💡 Hint

Think about what happens if required data for verification is not available.

If the biometric template is missing, the system cannot verify the user’s fingerprint, so authentication fails or returns an error.

❓ Comparison

advanced

Which authentication mechanism provides the strongest protection against password theft?

Compare these authentication methods and select the one that best protects against password theft.

A Multi-factor authentication using password and hardware token

B Single-factor password authentication

C Password authentication with periodic forced resets

D Password stored in hashed form on the server

💡 Hint

Consider which method adds an extra layer beyond just the password.

Multi-factor authentication combining a password and a hardware token requires both factors, making it much harder for attackers to gain access even if the password is stolen.

❓ Reasoning

expert

Why is storing passwords using salted hashes more secure than storing plain hashes?

Explain why adding a salt to password hashes improves security compared to storing just the hash of the password.

A Salting encrypts the password making it unreadable to the system

B Salting speeds up the authentication process by caching hashes

C Salting allows passwords to be stored in plain text safely

D Salting prevents attackers from using precomputed tables to reverse hashes easily

💡 Hint

Think about how attackers try to guess passwords using common hash lists.

Salting adds unique random data to each password before hashing, so attackers cannot use precomputed hash tables (rainbow tables) to reverse the hashes easily.