CAS-004 Security Engineering Practice Question
An organization wants to implement passwordless authentication using FIDO2/WebAuthn. Which of the following best describes the primary security advantage of this approach over traditional password-based authentication?
⚠ Common exam trap
The trap here is conflating 'passwordless' with 'no second factor' — candidates assume removing the password means removing MFA, when FIDO2 actually strengthens authentication by binding cryptographic credentials to the origin, which is the specific anti-phishing property the exam wants you to identify.
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
✓
It prevents phishing by using cryptographic keys bound to the origin
FIDO2/WebAuthn uses public-key cryptography where the private key never leaves the authenticator, and the credential is cryptographically bound to the origin (relying party ID) during registration. This origin binding means a phishing site on a different domain cannot trigger the authenticator to produce a valid assertion, because the browser enforces the RP ID match. Even if a user is tricked into visiting a lookalike site, the signature will not validate against the legitimate server's expected origin.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It eliminates the need for multi-factor authentication
Why it's wrong here
FIDO2/WebAuthn itself constitutes possession-plus-inherence authentication, so it satisfies rather than removes multi-factor requirements; the advantage is origin-bound credentials immune to phishing and replay. It tempts because passwordless is often described as replacing passwords, and would be correct if the question asked about single-factor password elimination.
- ✓
It prevents phishing by using cryptographic keys bound to the origin
Why this is correct
FIDO2/WebAuthn credentials are bound to the relying party's origin, and the authenticator signs a challenge with a private key that never leaves the device. A phishing site on a different origin cannot obtain a valid assertion, eliminating credential replay regardless of password reuse.
- ✗
It allows users to reuse the same password across services
Why it's wrong here
WebAuthn generates a unique public-private key pair per relying party, so credentials cannot be reused across services; the advantage is eliminating shared secrets vulnerable to credential stuffing. It tempts because password reuse is a familiar user behaviour, and would be correct if the question asked about reducing password fatigue.
- ✗
It requires a hardware token for every login
Why it's wrong here
FIDO2/WebAuthn permits platform authenticators such as Windows Hello or Touch ID, so hardware tokens are optional, not mandatory. It tempts because roaming security keys are a common FIDO2 form factor, and would be correct if the question asked which authenticator type resists phishing on shared devices.
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 and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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.