hardMultiple ChoiceObjective-mapped
CAS-004 An OpenVPN configuration file is shown Practice Question
Exhibit
Refer to the exhibit. Exhibit: ``` [openvpn] port 1194 proto udp dev tun ca ca.crt cert server.crt key server.key dh dh2048.pem tls-server tls-version-min 1.2 cipher AES-256-CBC auth SHA256 ```
An OpenVPN configuration file is shown. A security auditor recommends replacing the cipher and auth directives. Which of the following is the BEST replacement pair from a security engineering perspective?
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
✓
cipher AES-256-GCM and auth SHA256
Cipher AES-256-GCM and auth SHA256, is the best replacement pair. AES-256-GCM is an AEAD cipher that provides both confidentiality and integrity, making the auth directive redundant but still compatible with SHA256. AES-256-GCM is considered strong and current. Option B uses AES-128-GCM with SHA384; while still secure, AES-256 is generally preferred for higher security margins. Option C uses 3DES-168 and MD5, both of which are weak and deprecated. Option D uses Blowfish-128 and SHA1, where Blowfish is outdated and SHA1 is considered weak.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
cipher AES-256-GCM and auth SHA256
Why this is correct
AES-256-GCM is an AEAD cipher that includes authentication, so the auth directive becomes unnecessary; however, OpenVPN allows both. This is a secure modern combination.
- ✗
cipher AES-128-GCM and auth SHA384
Why it's wrong here
While GCM is good, AES-128 is less secure than AES-256; also auth SHA384 is stronger but unnecessary if GCM is used. The recommendation prefers stronger encryption.
- ✗
cipher 3DES-168 and auth MD5
Why it's wrong here
3DES is obsolete and vulnerable to meet-in-the-middle attacks; MD5 is cryptographically broken.
- ✗
cipher Blowfish-128 and auth SHA1
Why it's wrong here
Blowfish is relatively old and less efficient than AES; SHA1 is deprecated for security.
Quick reference
VPN Protocol Comparison
| Protocol | Port | Encryption | Authentication | Use Case |
|---|---|---|---|---|
| IKEv2 / IPsec | UDP 500 / 4500 | AES-256 | Certificates / PSK | Site-to-site & remote access |
| SSL / TLS VPN | TCP 443 | TLS 1.3 | Certificates / MFA | Clientless remote access |
| L2TP / IPsec | UDP 1701 | AES (IPsec) | PSK / Certificates | Legacy remote access |
| WireGuard | UDP 51820 | ChaCha20 | Public keys | Modern high-performance VPN |
| PPTP | TCP 1723 | MPPE (weak) | MS-CHAPv2 | Legacy — avoid in production |
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
Go deeper
Related to this question
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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.