- A
Mandatory forward secrecy using ephemeral Diffie-Hellman
TLS 1.3 requires ephemeral key exchanges (DHE or ECDHE) providing forward secrecy.
- B
Support for RSA key exchange
Why wrong: RSA key exchange is removed in TLS 1.3 due to lack of forward secrecy.
- C
Only server-side authentication
Why wrong: TLS 1.3 supports mutual authentication, but it is not mandatory.
- D
Use of RC4 for encryption
Why wrong: RC4 is deprecated and removed in TLS 1.3.
Question 392 of 1,000
CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network security. 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.
A company is implementing TLS 1.3 to secure web communications. Which of the following features is unique to TLS 1.3 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 using ephemeral Diffie-Hellman
TLS 1.3 (RFC 8446) mandates forward secrecy by requiring ephemeral Diffie-Hellman (DHE or ECDHE) key exchange for all handshakes. This ensures that session keys are never derived from long-term static keys, so compromising the server's private key does not compromise past session keys. Earlier TLS versions allowed static RSA key exchange, which lacks 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.
- ✓
Mandatory forward secrecy using ephemeral Diffie-Hellman
Why this is correct
TLS 1.3 requires ephemeral key exchanges (DHE or ECDHE) providing forward secrecy.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Support for RSA key exchange
Why it's wrong here
RSA key exchange is removed in TLS 1.3 due to lack of forward secrecy.
- ✗
Only server-side authentication
Why it's wrong here
TLS 1.3 supports mutual authentication, but it is not mandatory.
- ✗
Use of RC4 for encryption
Why it's wrong here
RC4 is deprecated and removed in TLS 1.3.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse 'mandatory forward secrecy' with optional forward secrecy in earlier TLS versions, or mistakenly think RSA key exchange is still supported in TLS 1.3.
Detailed technical explanation
How to think about this question
Under the hood, TLS 1.3 reduces the handshake to one round trip (0-RTT for resumption) and eliminates static key exchanges. The ephemeral keys are generated per session and discarded after use, ensuring that even if the server's long-term signing key is later stolen, past session keys remain secure. In real-world scenarios, this protects against mass decryption attacks like those possible with static RSA in TLS 1.2.
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 using ephemeral Diffie-Hellman — TLS 1.3 (RFC 8446) mandates forward secrecy by requiring ephemeral Diffie-Hellman (DHE or ECDHE) key exchange for all handshakes. This ensures that session keys are never derived from long-term static keys, so compromising the server's private key does not compromise past session keys. Earlier TLS versions allowed static RSA key exchange, which lacks 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.
About these practice questions
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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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