CISSP Communication and Network Security Practice Question
A security engineer is evaluating VPN protocols for a remote access solution. The requirements are: strong encryption with perfect forward secrecy, support for mutual authentication, and no reliance on pre-shared keys that could be brute-forced. Which protocol best meets these requirements?
⚠ Common exam trap
A common misconception is that IPsec with IKEv2 is always secure regardless of authentication method, but the trap here is that pre-shared keys (even with IKEv2) violate the 'no reliance on pre-shared keys' requirement and can be brute-forced if weak, whereas WireGuard's public-key-based mutual authentication avoids this vulnerability entirely.
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
✓
WireGuard
WireGuard is the correct choice because it uses modern cryptographic primitives (Curve25519, ChaCha20, Poly1305, BLAKE2s) that inherently provide perfect forward secrecy via ephemeral Diffie-Hellman key exchanges, supports mutual authentication through public-key-based handshakes, and eliminates pre-shared keys as the sole authentication factor—though an optional PSK can be added for post-quantum resistance, it is not required and does not weaken security if omitted.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
L2TP/IPsec with pre-shared keys
Why it's wrong here
Pre-shared keys in L2TP/IPsec are symmetric secrets shared by all peers; compromise or brute force breaks mutual authentication and PFS is not guaranteed. It is tempting for simple site-to-site setups. Certificate-based IKEv2 satisfies the stated requirements without shared secrets.
- ✗
PPTP with MS-CHAPv2
Why it's wrong here
PPTP's MS-CHAPv2 authentication is cryptographically broken and PPTP provides no perfect forward secrecy, failing both requirements. It is tempting for legacy client compatibility. A protocol such as IKEv2 with certificate-based authentication delivers PFS and mutual authentication without pre-shared keys.
- ✓
WireGuard
Why this is correct
WireGuard uses Curve25519 for key exchange, providing perfect forward secrecy without pre-shared keys, and supports mutual authentication via public-key cryptography. Its Noise protocol framework underpins these guarantees, satisfying the stem's three constraints: strong encryption, PFS, and no brute-forceable PSKs.
- ✗
IPsec with IKEv2 using pre-shared keys
Why it's wrong here
IKEv2 with pre-shared keys still relies on a shared secret, which the requirements explicitly exclude because it can be brute-forced; PFS also depends on key exchange configuration. It is tempting because IKEv2 itself is strong. Certificate-based authentication removes the shared-secret weakness.
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
Learn chapter
Access Control Models and Mechanisms
Key term
Encryption
Encryption is the process of converting readable data into a secret code to prevent unauthorized access.
Key term
Security
Security in IT is the practice of protecting systems, networks, and data from unauthorized access, damage, or theft.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CISSP practice question is part of Courseiva's free ISC2 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 CISSP exam.