CAS-004 Security Engineering Practice Question
An IoT device manufacturer wants to ensure that firmware updates are authentic and have not been tampered with. The device has limited computational resources. Which cryptographic primitive is most appropriate for verifying the integrity and authenticity of firmware images?
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
✓
Digital signature using ECDSA P-384
Digital signatures provide both integrity and authenticity. RSA is too computationally intensive for constrained devices; ECDSA or Ed25519 are more suitable. The question asks for the primitive, so digital signatures is the correct category.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Digital signature using ECDSA P-384
Why this is correct
Digital signatures provide non-repudiation and authenticity without shared secrets; ECDSA is efficient for constrained devices.
- ✗
SHA-256 hash only
Why it's wrong here
A hash provides integrity but no authenticity; an attacker can replace both firmware and hash.
- ✗
Symmetric MAC using AES-256-GCM
Why it's wrong here
A MAC provides integrity and authenticity but requires a shared secret, which is less manageable for firmware distribution.
- ✗
HMAC-SHA256 with a device-specific key
Why it's wrong here
HMAC provides integrity and authenticity but requires key management for each device, which is less scalable for firmware distribution.
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.