Short Answer 
Two-factor authentication (2FA) enhances security by requiring two different verification methods, combining something known (password) and something possessed (mobile device). Valid combinations include a password with a PIN or a CAC with a PIN, while invalid combinations consist of two possession factors or two biometric methods.
Step 1: Understand Two-Factor Authentication
Two-factor authentication (2FA) enhances security by requiring two distinct methods to verify a user’s identity. This process combines something you know (like a password) with something you have (like a mobile device or CAC). Implementing 2FA reduces the risk of unauthorized access significantly, making it a critical security measure.
Step 2: Identify Valid Combinations
When examining different options for 2FA, it’s important to identify combinations that meet the criteria. Valid combinations include:
- Password and Personal Identification Number (PIN): This utilizes knowledge and possession factors, making it a proper 2FA setup.
- Common Access Card (CAC) and Personal Identification Number (PIN): Here, the CAC acts as a token, and the PIN serves as a knowledge factor, also making it valid.
Step 3: Understand Invalid Combinations
Not all combinations qualify as effective two-factor authentication. Consider the following:
- Security token and Common Access Card (CAC): Both are possession factors, failing to include a knowledge factor.
- Fingerprint and facial recognition: Both are biometric and do not provide two different types of verification, making this option invalid.