hardMultiple Choice
CAS-004 Practice Question: An architect is designing a multi-factor…
An architect is designing a multi-factor authentication (MFA) solution for remote access. Which of the following is the STRONGEST form of second factor?
⚠ Common exam trap
CompTIA often tests the misconception that SMS OTP or email OTP is 'strong enough' for remote access, but the trap here is that candidates overlook the fundamental security advantage of hardware-bound private keys over shared-secret OTPs, especially against phishing and relay attacks.
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 hardware token
FIDO2 WebAuthn hardware tokens provide the strongest second factor because they use public-key cryptography to generate a unique key pair per service, with the private key stored securely on the token. This eliminates phishing, man-in-the-middle, and replay attacks, as the token signs a challenge from the relying party without ever sharing a shared secret over the network.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Email OTP
Why it's wrong here
Email OTP is delivered to a mailbox that is typically protected by the same password being verified, so compromise of that credential yields both factors. It is genuinely useful for low-risk consumer account recovery where no hardware token is issued, but it provides no phishing-resistant cryptographic binding to the authentication session.
- ✓
FIDO2 WebAuthn hardware token
Why this is correct
FIDO2 WebAuthn binds authentication to the origin via public-key cryptography, so credentials cannot be phished or replayed. This satisfies the demand for the strongest second factor, since possession-based hardware tokens with origin binding outperform OTP codes and push notifications against real-time relay attacks.
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SMS one-time code
Why it's wrong here
SMS one-time codes are vulnerable to SIM-swap, SS7 interception and real-time relay phishing, so the code can be captured and replayed within its validity window. SMS remains a pragmatic fallback for users without smartphones or tokens, but it is not phishing-resistant and cannot bind the factor cryptographically to the session.
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Knowledge-based questions
Why it's wrong here
Knowledge-based questions rely on static personal data that is often discoverable through social media, breaches or public records, so an attacker can answer them without possessing a device. They suit account-recovery flows where no token exists, but they are replayable shared secrets rather than a possession factor bound to the session.
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.