CAS-004 Security Engineering Practice Question
Which key exchange algorithm provides perfect forward secrecy (PFS) and is recommended for use in TLS 1.3?
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
✓
ECDHE
ECDHE (Elliptic Curve Diffie-Hellman Ephemeral) provides PFS as session keys are ephemeral.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
ECDHE
Why this is correct
ECDHE generates ephemeral keys, ensuring PFS.
- ✗
RSA key exchange
Why it's wrong here
RSA does not provide PFS.
- ✗
Pre-shared key (PSK)
Why it's wrong here
PSK alone does not provide PFS.
- ✗
Diffie-Hellman (DH)
Why it's wrong here
DH can be used with ephemeral keys (DHE) but the question asks for recommended; ECDHE is preferred.
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.