CAS-004 Security Engineering Practice Question
An enterprise is deploying a multi-factor authentication (MFA) solution. The security team requires a factor that is resistant to phishing and does not rely on shared secrets. Which of the following MFA types BEST meets this requirement?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
FIDO2/WebAuthn security keys
FIDO2/WebAuthn uses public-key cryptography, with the private key stored on the device, and the protocol is designed to be phishing-resistant by binding credentials to the origin. TOTP/HOTP rely on shared secrets and are vulnerable to phishing. Hardware tokens like YubiKey can implement FIDO2. Biometrics are a factor but not inherently phishing-resistant alone.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Biometric fingerprint scanner
Why it's wrong here
Biometrics alone do not provide phishing resistance and can be spoofed.
- ✗
SMS one-time passcodes
Why it's wrong here
SMS is vulnerable to interception and phishing.
- ✓
FIDO2/WebAuthn security keys
Why this is correct
FIDO2 uses public-key cryptography and is phishing-resistant.
- ✗
TOTP via authenticator app
Why it's wrong here
TOTP is vulnerable to phishing as the code can be intercepted.
Quick reference
Asymmetric Encryption Algorithm Comparison
| Algorithm | Key Exchange | Signatures | Equivalent Security Key | Notes |
|---|---|---|---|---|
| RSA-3072 | Yes | Yes | 128-bit | Widely deployed; slow for bulk data |
| ECDSA P-256 | No | Yes | 128-bit | Fast signatures; standard TLS certs |
| ECDH / ECDHE | Yes | No | 128-bit | Perfect forward secrecy in TLS 1.3 |
| DH / DHE | Yes | No | 128-bit (3072-bit key) | Replaced by ECDHE in modern TLS |
| Ed25519 | No | Yes | ~128-bit | SSH keys, modern PKI |
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CAS-005 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CAS-005 exam.