- A
Backward compatibility with SSL 3.0
Why wrong: SSL 3.0 is deprecated and not supported in TLS 1.3.
- B
Use of RSA key exchange for authentication
Why wrong: RSA key exchange is removed in TLS 1.3.
- C
Support for RC4 stream cipher
Why wrong: RC4 is deprecated and removed in TLS 1.3.
- D
Mandatory forward secrecy via ephemeral Diffie-Hellman
TLS 1.3 requires PFS; all key exchanges use ephemeral keys.
Question 199 of 1,000
CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network security. 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.
Which of the following is a key feature of TLS 1.3 that enhances security compared to earlier versions?
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
✓
Mandatory forward secrecy via ephemeral Diffie-Hellman
TLS 1.3 mandates forward secrecy by requiring ephemeral Diffie-Hellman (DHE or ECDHE) key exchange for all sessions. This ensures that even if a server's long-term private key is compromised, past session keys cannot be derived, protecting historical communications. In contrast, earlier TLS versions allowed static RSA key exchange, which does not provide forward secrecy.
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.
- ✗
Backward compatibility with SSL 3.0
Why it's wrong here
SSL 3.0 is deprecated and not supported in TLS 1.3.
- ✗
Use of RSA key exchange for authentication
Why it's wrong here
RSA key exchange is removed in TLS 1.3.
- ✗
Support for RC4 stream cipher
Why it's wrong here
RC4 is deprecated and removed in TLS 1.3.
- ✓
Mandatory forward secrecy via ephemeral Diffie-Hellman
Why this is correct
TLS 1.3 requires PFS; all key exchanges use ephemeral keys.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may associate 'forward secrecy' only with optional configurations in TLS 1.2, not realizing that TLS 1.3 makes it mandatory and eliminates static RSA entirely, which is a key architectural change defined in RFC 8446.
Detailed technical explanation
How to think about this question
Under the hood, TLS 1.3 reduces the handshake to one round trip (1-RTT) by combining key exchange and authentication into a single flight, using (EC)DHE parameters signed by the server's certificate. The mandatory ephemeral key exchange means each session generates a unique, temporary Diffie-Hellman key pair, and the pre-master secret is derived from the ephemeral keys, not the static server private key. In real-world scenarios, this prevents an attacker who later obtains a server's private key (e.g., via Heartbleed-like leaks) from decrypting previously recorded TLS traffic.
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
Asymmetric Encryption Algorithm Comparison
| Algorithm | Key Exchange | Signatures | Equivalent Security Key | Notes |
|---|---|---|---|---|
| RSA-3072 | Yes | Yes | 128-bit | Widely deployed; slow for bulk data |
| ECDSA P-256 | No | Yes | 128-bit | Fast signatures; standard TLS certs |
| ECDH / ECDHE | Yes | No | 128-bit | Perfect forward secrecy in TLS 1.3 |
| DH / DHE | Yes | No | 128-bit (3072-bit key) | Replaced by ECDHE in modern TLS |
| Ed25519 | No | Yes | ~128-bit | SSH keys, modern PKI |
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 CISSP question test?
Communication and Network Security — This question tests Communication and Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Mandatory forward secrecy via ephemeral Diffie-Hellman — TLS 1.3 mandates forward secrecy by requiring ephemeral Diffie-Hellman (DHE or ECDHE) key exchange for all sessions. This ensures that even if a server's long-term private key is compromised, past session keys cannot be derived, protecting historical communications. In contrast, earlier TLS versions allowed static RSA key exchange, which does not provide forward secrecy.
What should I do if I get this CISSP 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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Last reviewed: Jul 4, 2026
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.
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