The answer is Diffie-Hellman Ephemeral (DHE), the correct key exchange method for ensuring forward secrecy. DHE achieves this by generating a fresh, temporary key pair for each session and never reusing the private key, so even if an attacker later compromises the server’s long-term static key, they cannot decrypt previously recorded traffic because the ephemeral session keys have been destroyed. On the Systems Security Certified Practitioner (SSCP) exam, this concept tests your understanding of cryptographic protocols and their security properties; a common trap is confusing static Diffie-Hellman (which reuses keys and lacks forward secrecy) with DHE. Remember the memory tip: “DHE = Destroyed keys, History safe, Ephemeral.”
SSCP Cryptography Practice Question
This SSCP practice question tests your understanding of cryptography. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 wants to implement a cryptographic solution that ensures forward secrecy for its internal communications. Which key exchange method should be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
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Diffie-Hellman Ephemeral (DHE)
DHE (Diffie-Hellman Ephemeral) generates a fresh, temporary key pair for each session and never reuses the private key, ensuring that compromise of a long-term key does not expose past session keys. This provides forward secrecy because the ephemeral keys are destroyed after the session ends, making it computationally infeasible to decrypt recorded traffic even if the server's static key is later compromised.
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.
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RSA key exchange
Why it's wrong here
RSA key exchange uses the server's long-term private key; compromise leaks past sessions.
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Elliptic Curve Diffie-Hellman (ECDH)
Why it's wrong here
ECDH without ephemeral keys does not guarantee forward secrecy.
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Diffie-Hellman Ephemeral (DHE)
Why this is correct
DHE generates temporary keys each session, so compromise of long-term keys does not expose past sessions.
Related concept
Read the scenario before looking for a memorised answer.
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Static Diffie-Hellman
Why it's wrong here
Static DH uses fixed keys and does not provide forward secrecy.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the distinction between 'Diffie-Hellman' (which can be static) and 'Diffie-Hellman Ephemeral' (DHE) — the trap is that candidates see 'Diffie-Hellman' and assume forward secrecy, forgetting that only the ephemeral variant provides it.
Detailed technical explanation
How to think about this question
In DHE, the server generates a fresh Diffie-Hellman private key and public value for each TLS handshake, signed with its long-term certificate to authenticate the exchange. The ephemeral private key is discarded immediately after the session key is derived, so even if an attacker obtains the server's long-term signing key, they cannot recover the ephemeral private key to decrypt past traffic. This is defined in RFC 5246 (TLS 1.2) and is a key requirement for compliance with standards like PCI DSS and NIST SP 800-52.
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.
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.
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: Diffie-Hellman Ephemeral (DHE) — DHE (Diffie-Hellman Ephemeral) generates a fresh, temporary key pair for each session and never reuses the private key, ensuring that compromise of a long-term key does not expose past session keys. This provides forward secrecy because the ephemeral keys are destroyed after the session ends, making it computationally infeasible to decrypt recorded traffic even if the server's static key is later compromised.
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.
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Question Discussion
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