- A
Ephemeral Diffie-Hellman (DHE or ECDHE)
Ephemeral DH generates new key pairs for each session, so compromise of long-term keys does not expose past session keys.
- B
RSA key exchange
Why wrong: RSA key exchange does not provide forward secrecy because the session key is encrypted with the server's RSA private key; if that key is compromised, past sessions can be decrypted.
- C
Pre-shared key (PSK)
Why wrong: PSK is a symmetric key; if compromised, all past sessions using that key are exposed.
- D
Static Diffie-Hellman
Why wrong: Static DH uses fixed private keys; if the private key is compromised, all past session keys can be derived.
Question 123 of 1,000
SSCP Cryptography Practice Question
This SSCP practice question tests your understanding of cryptography. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
An organization is configuring a VPN using IPsec. To ensure forward secrecy, which key exchange method should be used?
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 forward secrecy because it generates a temporary, one-time key pair for each session. If the long-term private key is compromised, past session keys cannot be derived, as the ephemeral keys are discarded after use. This ensures that even if an attacker records encrypted traffic and later obtains the private key, they cannot decrypt past sessions.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Ephemeral Diffie-Hellman (DHE or ECDHE)
Why this is correct
Ephemeral DH generates new key pairs for each session, so compromise of long-term keys does not expose past session keys.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
RSA key exchange
Why it's wrong here
RSA key exchange does not provide forward secrecy because the session key is encrypted with the server's RSA private key; if that key is compromised, past sessions can be decrypted.
- ✗
Pre-shared key (PSK)
Why it's wrong here
PSK is a symmetric key; if compromised, all past sessions using that key are exposed.
- ✗
Static Diffie-Hellman
Why it's wrong here
Static DH uses fixed private keys; if the private key is compromised, all past session keys can be derived.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'Diffie-Hellman' in general with forward secrecy, not realizing that only the ephemeral variant (DHE/ECDHE) provides it, while static Diffie-Hellman does not.
Detailed technical explanation
How to think about this question
In IPsec, DHE (Diffie-Hellman Ephemeral) generates a new Diffie-Hellman key pair for each IKE phase 1 or phase 2 negotiation, using groups like modp1024 (group 2) or modp2048 (group 14). The ephemeral private key is securely deleted after the session key is derived, ensuring that even if the IKE authentication key (e.g., from a PSK or certificate) is later compromised, the derived session keys remain secure. In practice, this is critical for compliance with standards like PCI DSS, which require forward secrecy for VPN connections.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A developer is choosing between AES-256 (symmetric) and RSA-2048 (asymmetric) for encrypting a large file that will be sent to a partner. Symmetric encryption is fast but requires key exchange; asymmetric is slower but solves the key distribution problem. A hybrid approach — encrypt the file with AES, encrypt the AES key with RSA — is standard. Questions like this test whether you understand when each approach applies.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this SSCP question test?
Cryptography — This question tests Cryptography — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Ephemeral Diffie-Hellman (DHE or ECDHE) — Ephemeral Diffie-Hellman (DHE or ECDHE) provides forward secrecy because it generates a temporary, one-time key pair for each session. If the long-term private key is compromised, past session keys cannot be derived, as the ephemeral keys are discarded after use. This ensures that even if an attacker records encrypted traffic and later obtains the private key, they cannot decrypt past sessions.
What should I do if I get this SSCP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jul 4, 2026
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.
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