CAS-004 Security Architecture Practice Question
A security architect is designing a cryptographic system for a government agency that must protect classified data for the next 30 years. The agency is concerned about the threat from quantum computers. Which NIST post-quantum cryptography algorithm is recommended for key encapsulation?
⚠ Common exam trap
The trap is mixing up the two CRYSTALS algorithms — candidates see 'CRYSTALS' and pick Dilithium, forgetting that Kyber is the KEM and Dilithium is the signature scheme.
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
✓
CRYSTALS-Kyber
CRYSTALS-Kyber is the NIST-selected post-quantum algorithm for key encapsulation (KEM), standardized as FIPS 203 (ML-KEM). It is designed to resist attacks from both classical and quantum computers, making it appropriate for long-lived classified data. CRYSTALS-Dilithium is for digital signatures, not key encapsulation, and the classical algorithms (ECDH, RSA) are vulnerable to Shor's algorithm on a sufficiently powerful quantum computer.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
ECDH with NIST P-384
Why it's wrong here
ECDH with P-384 relies on elliptic-curve discrete logarithms, which Shor's algorithm breaks on a sufficiently large quantum computer, so it cannot protect data for 30 years. It is tempting because P-384 is approved for classified Suite B use today, and would be correct for conventional key agreement against classical attackers.
- ✓
CRYSTALS-Kyber
Why this is correct
CRYSTALS-Kyber is a lattice-based key encapsulation mechanism selected by NIST for post-quantum standardisation, resisting attacks from both classical and quantum computers. Its Module-LWE hardness underpins the 30-year confidentiality requirement, unlike RSA or ECC, which Shor's algorithm breaks.
- ✗
CRYSTALS-Dilithium
Why it's wrong here
CRYSTALS-Dilithium is a digital signature scheme, so it provides authentication and integrity, not the shared secret required for key encapsulation. It is tempting because it is a NIST post-quantum standard and lattice-based like ML-KEM; it would be correct for signing firmware, certificates or code.
- ✗
RSA-4096
Why it's wrong here
RSA-4096 depends on integer factorisation, which Shor's algorithm solves on a sufficiently large quantum computer, so it cannot protect data for 30 years. It is tempting because 4096-bit RSA is widely deployed and considered strong against classical attack; it would be correct for conventional key transport today.
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 and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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.