SSCP Cryptography Practice Question
A company is deploying a VPN using IPsec. They want to ensure that even if the private key of the server is compromised, past session keys cannot be derived. Which key exchange method should they use?
⚠ Common exam trap
It's easy for candidates to confuse authentication with key exchange, assuming that RSA or static DH provides PFS because they involve public-key cryptography, but only ephemeral DH ensures that session keys are not derived from long-term secrets.
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
✓
Ephemeral Diffie-Hellman (DHE or ECDHE)
Ephemeral Diffie-Hellman (DHE or ECDHE) provides perfect forward secrecy (PFS) because it generates a unique, temporary session key for each session using ephemeral key pairs. Even if the server's long-term private key is compromised, past session keys cannot be derived because they were created from ephemeral keys that are discarded after each session. This ensures that historical encrypted traffic remains secure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Pre-shared key (PSK)
Why it's wrong here
PSK is static and does not provide forward secrecy.
- ✗
RSA key exchange
Why it's wrong here
RSA key exchange does not provide forward secrecy as the session key is encrypted with the server's static key.
- ✓
Ephemeral Diffie-Hellman (DHE or ECDHE)
Why this is correct
Ephemeral key exchange ensures that session keys are temporary and not linked to long-term keys.
- ✗
Diffie-Hellman with static keys
Why it's wrong here
Static DH does not provide forward secrecy.
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
About these practice questions
Courseiva writes every SSCP question from scratch — 920 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SSCP 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 SSCP exam.