CAS-004 Security Engineering Practice Question
A security architect is designing a new web application that must meet strict data confidentiality and integrity requirements. The application will run in a cloud environment and must support low-latency operations. The architect is considering cipher suites for TLS 1.3. Which combination of algorithms would best meet these requirements?
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
✓
ChaCha20-Poly1305 with ECDHE key exchange and Ed25519
ChaCha20-Poly1305 is a symmetric cipher that offers excellent performance on mobile and low-power devices, while providing authenticated encryption. ECDHE provides forward secrecy, and Ed25519 provides efficient authentication. AES-256-GCM is also good but ChaCha20 often performs better in software. RSA key exchange does not provide forward secrecy. SHA-256 is a hashing algorithm, not an encryption algorithm.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
AES-128-CBC with HMAC-SHA256 and RSA-2048
Why it's wrong here
CBC mode does not provide authenticated encryption, and RSA-2048 is weaker than recommended.
- ✗
ChaCha20-Poly1305 with static ECDH and SHA-384
Why it's wrong here
Static ECDH does not provide forward secrecy.
- ✓
ChaCha20-Poly1305 with ECDHE key exchange and Ed25519
Why this is correct
This combination provides authenticated encryption, forward secrecy, and efficient authentication suitable for low-latency requirements.
- ✗
AES-256-GCM with RSA key exchange and SHA-256
Why it's wrong here
RSA key exchange does not provide forward secrecy, and AES-256-GCM may have higher latency in some environments.
Quick reference
Symmetric Encryption Algorithm Comparison
| Algorithm | Key Size | Block Size | Status | Notes |
|---|---|---|---|---|
| AES-128 | 128-bit | 128-bit | Current standard | NIST approved; WPA3, TLS |
| AES-256 | 256-bit | 128-bit | Current standard | Preferred for sensitive / govt data |
| 3DES | 112-bit effective | 64-bit | Deprecated (2023) | Replaced by AES |
| DES | 56-bit | 64-bit | Broken | Cracked in < 24 h; never deploy |
| ChaCha20 | 256-bit | Stream cipher | Current | TLS 1.3, WireGuard |
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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.