CAS-004 Security Engineering Practice Question
A company is deploying IoT sensors in a harsh environment. The sensors have limited processing power and memory. Which of the following cryptographic algorithms is most suitable for ensuring data confidentiality with minimal overhead?
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
ChaCha20-Poly1305 is a stream cipher that is fast in software, especially on devices without AES hardware acceleration, and provides authenticated encryption with low overhead.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
RSA-4096
Why it's wrong here
RSA-4096 is asymmetric and its large key sizes and modular exponentiation demand far more processing and memory than constrained sensors can spare. It is tempting because RSA is a genuine confidentiality algorithm, and would suit key exchange or signatures on capable hardware.
- ✓
ChaCha20-Poly1305
Why this is correct
ChaCha20-Poly1305 is a stream cipher with AEAD that runs efficiently in software without AES hardware acceleration, suiting constrained IoT processors. Its low memory footprint and fast performance deliver confidentiality and integrity with minimal overhead in harsh environments.
- ✗
SHA-256
Why it's wrong here
SHA-256 is a hash function providing integrity, not confidentiality, so it cannot encrypt sensor data at all. It is tempting because it is fast and lightweight, which matches the constrained device profile, but hashing is not encryption.
- ✗
AES-256-GCM
Why it's wrong here
AES-256-GCM is a symmetric block cipher requiring more memory and processing than lightweight ciphers, straining constrained IoT sensors. It is tempting because GCM provides authenticated encryption widely trusted in general computing. For limited-power devices, a lightweight algorithm such as ASCON or ChaCha20-Poly1305 is the correct choice.
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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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.