CAS-004 Security Engineering Practice Question
A company is deploying a new authentication system that leverages FIDO2/WebAuthn. Security architects want to ensure that the private key never leaves the authenticator device. Which attack vector is mitigated by this approach?
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
✓
Server-side database breach exposing credentials
FIDO2/WebAuthn uses public-key cryptography where the private key is generated on the authenticator and never exported. This prevents server-side database breaches from compromising private keys, as there are no shared secrets stored on the server.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Man-in-the-middle attacks on TLS
Why it's wrong here
TLS protects the channel, but FIDO2 does not directly mitigate MiTM on TLS.
- ✓
Server-side database breach exposing credentials
Why this is correct
Since no private keys or secrets are stored on the server, a breach does not expose authentication secrets.
- ✗
Replay attacks on authentication tokens
Why it's wrong here
Replay attacks are mitigated by challenge-response, not by private key non-exportability.
- ✗
Phishing attacks
Why it's wrong here
While FIDO2 reduces phishing by binding credentials to origin, the key non-exportability specifically addresses server breaches.
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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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