CAS-004 Security Engineering and Cryptography Practice Question
This CAS-004 practice question tests your understanding of security engineering and cryptography. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
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.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CAS-004 NAT questions on configuration and troubleshooting.
Security Engineering and Cryptography — This question tests Security Engineering and Cryptography — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this CAS-004 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CAS-004 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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