CAS-004 Security Architecture Practice Question
An organization is planning to modernize its cryptographic infrastructure to protect sensitive data for the next 10 years. The security architect must consider future threats from quantum computing. Which TWO quantum-resistant algorithms should the architect prioritize for key encapsulation and digital signatures? (Choose TWO.)
⚠ Common exam trap
CAS-005 often tests the confusion between symmetric encryption (like AES) and asymmetric algorithms for key encapsulation and digital signatures, or assumes that increasing key size of classical algorithms (RSA, ECDSA) provides quantum resistance, which is false.
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-Dilithium
CRYSTALS-Dilithium (A) is correct because it is a NIST-selected post-quantum digital signature algorithm based on lattice cryptography, designed to resist attacks from both classical and quantum computers, making it suitable for long-term signing needs. CRYSTALS-Kyber (E) is correct because it is the NIST-selected post-quantum key encapsulation mechanism (KEM), also lattice-based, intended for establishing shared secrets resistant to quantum cryptanalysis. Together they cover the two required functions: Kyber for key encapsulation and Dilithium for digital signatures. AES-256 with GCM (B) is a symmetric cipher and does not provide quantum-resistant key encapsulation or signatures, though symmetric keys are less affected by quantum attacks. ECDSA with P-521 (C) and RSA-4096 (D) are classical asymmetric algorithms whose security would be broken by Shor's algorithm on a sufficiently large quantum computer, so they are not quantum-resistant.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
CRYSTALS-Dilithium
Why this is correct
CRYSTALS-Dilithium is a lattice-based post-quantum signature scheme, selected by NIST for digital signatures. It resists Shor's algorithm attacks on RSA and ECC, satisfying the digital signature half of the quantum-resistant requirement for long-term data protection.
- ✗
AES-256 with GCM
Why it's wrong here
AES-256-GCM is a symmetric cipher for bulk data confidentiality and integrity, not a quantum-resistant key encapsulation or signature algorithm. It is tempting because AES-256 is considered quantum-resistant for symmetric use, but the question asks specifically for post-quantum KEM and signature primitives such as ML-KEM and ML-DSA.
- ✗
ECDSA with P-521
Why it's wrong here
ECDSA with P-521 relies on elliptic-curve discrete logarithms, which Shor's algorithm on a quantum computer breaks, so it provides no post-quantum signature assurance. It is tempting because P-521 offers the highest classical ECDSA strength, but that strength does not extend to quantum adversaries.
- ✗
RSA-4096
Why it's wrong here
RSA-4096 depends on integer factorisation, which Shor's algorithm solves efficiently on a sufficiently large quantum computer, so it cannot protect data for ten years. It is tempting because RSA-4096 is the strongest classical RSA key size, but key length does not confer quantum resistance.
- ✓
CRYSTALS-Kyber
Why this is correct
CRYSTALS-Kyber is a lattice-based key encapsulation mechanism, standardised by NIST for general encryption. It secures symmetric key exchange against quantum cryptanalysis, satisfying the key encapsulation half of the requirement for protecting sensitive data over the next decade.
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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About these practice questions
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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.