CAS-004 Security Engineering Practice Question
A company is implementing a passwordless authentication solution using FIDO2/WebAuthn. What is the primary security advantage of this approach over traditional password-based authentication?
⚠ Common exam trap
The trap is selecting 'eliminates the need for multi-factor authentication' because candidates conflate passwordless with single-factor; in reality, FIDO2 can be one factor and the core advantage tested is phishing resistance via cryptographic origin binding.
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 attacks by using cryptographic keys.
FIDO2/WebAuthn uses public-key cryptography where the private key never leaves the authenticator (e.g., a security key or platform authenticator), and the origin is cryptographically bound to the credential. This origin binding means a phishing site with a different domain cannot trigger the authenticator to sign the challenge, effectively preventing credential phishing. Traditional passwords, by contrast, can be captured and replayed by phishing proxies.
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 allows users to share passwords securely.
Why it's wrong here
FIDO2/WebAuthn credentials are asymmetric key pairs held in the authenticator; the private key never leaves the device and cannot be shared or phished, so password sharing is impossible. It is tempting because sharing credentials is a common password problem, but WebAuthn removes the shared secret entirely rather than securing it.
- ✗
It reduces server storage requirements.
Why it's wrong here
FIDO2/WebAuthn stores a public key on the server, so storage is not eliminated and is not the security advantage sought. It is tempting because removing password hashes does reduce some server-side data, but the question asks for the primary security benefit, which is resistance to phishing and credential replay.
- ✗
It eliminates the need for multi-factor authentication.
Why it's wrong here
FIDO2/WebAuthn replaces the password with a cryptographic key pair bound to the origin, but it does not remove the need for MFA; the authenticator itself is possession-based, and a PIN or biometric unlocks it. It is tempting because passwordless and MFA are often discussed together, yet they address different factors.
- ✓
It prevents phishing attacks by using cryptographic keys.
Why this is correct
FIDO2/WebAuthn binds the credential's private key to the relying party's origin, so a phishing site on a different domain cannot invoke it. This origin-scoped cryptographic assertion removes the shared-secret replay weakness inherent in password-based authentication.
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 |
About these practice questions
This CAS-005 question is part of Courseiva's 973-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
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.