CAS-004 Security Engineering Practice Question
A security engineer is configuring SSH for a jump host used to access critical servers. The engineer wants to restrict the cryptographic algorithms to the most secure options. Which of the following should be DISABLED?
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
✓
Diffie-Hellman group-exchange with SHA-1
Diffie-Hellman group-exchange with SHA-1 is weak and should be disabled in favor of stronger key exchange algorithms.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Diffie-Hellman group-exchange with SHA-1
Why this is correct
SHA-1 is deprecated due to collision attacks.
- ✗
AES-256-CTR
Why it's wrong here
AES-256-CTR is a strong cipher.
- ✗
Ed25519 for host keys
Why it's wrong here
Ed25519 is a strong public key algorithm.
- ✗
HMAC-SHA2-256
Why it's wrong here
This is a strong HMAC algorithm.
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.