CISSP Communication and Network Security Practice Question
Which of the following is a key feature of TLS 1.3 that enhances security compared to earlier versions?
⚠ Common exam trap
Many candidates confuse 'forward secrecy' with 'encryption strength' or 'cipher support,' and may incorrectly think that simply using a strong cipher like AES provides forward secrecy, when in fact it is the key exchange mechanism (ephemeral vs. static) that determines whether past sessions remain secure after key compromise.
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
TLS 1.3 mandates forward secrecy by requiring ephemeral Diffie-Hellman (DHE or ECDHE) key exchange for all sessions, eliminating static RSA and static DH key exchanges. This ensures that even if the server's long-term private key is compromised, past session keys cannot be derived, protecting historical traffic. Earlier TLS versions allowed static key exchanges, making them vulnerable to retrospective decryption.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Support for RC4 encryption
Why it's wrong here
RC4 is a stream cipher that was widely used in older TLS versions but has been explicitly removed from TLS 1.3. Its removal is due to significant cryptographic weaknesses, including biases in its keystream generation, which made it susceptible to various attacks like the "Bar Mitzvah" attack. TLS 1.3 mandates the use of modern, authenticated encryption with associated data (AEAD) ciphers, rendering RC4 obsolete and insecure for contemporary secure communications.
- ✗
Support for DES and 3DES
Why it's wrong here
DES (Data Encryption Standard) and its successor, 3DES (Triple DES), are symmetric block ciphers that have been deprecated and removed from TLS 1.3. DES, with its small 56-bit key, is easily breakable, while 3DES, despite its triple encryption, suffers from a small block size (64-bit). This small block size makes 3DES vulnerable to birthday attacks, such as the SWEET32 attack, which can recover plaintext from large volumes of encrypted data, thus compromising confidentiality.
- ✓
Mandatory forward secrecy
Why this is correct
Mandatory forward secrecy is a cornerstone security feature enforced by TLS 1.3, significantly enhancing protection against future compromise. This is achieved by requiring the use of ephemeral Diffie-Hellman (DHE) or Elliptic Curve Diffie-Hellman Ephemeral (ECDHE) key exchange mechanisms. Consequently, even if a server's long-term private key is compromised at a later date, an attacker cannot decrypt previously recorded session traffic because the session keys were unique and discarded after use, ensuring past communications remain confidential.
- ✗
Use of static RSA key exchange
Why it's wrong here
The use of static RSA key exchange has been completely removed in TLS 1.3 due to its critical security flaw: the lack of forward secrecy. With static RSA, the same private key is used to derive session keys for multiple sessions, meaning that if the server's long-term private key is ever compromised, all past communications encrypted using that key could be retroactively decrypted. TLS 1.3 exclusively mandates ephemeral key exchange methods like DHE or ECDHE to ensure that session keys are unique and temporary.
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 |
Go deeper
Related to this question
Learn chapter
Security Governance and Principles
Key term
Security
Security in IT is the practice of protecting systems, networks, and data from unauthorized access, damage, or theft.
Key term
TLS
Transport Layer Security (TLS) is a cryptographic protocol that encrypts data sent over the internet to keep it private and ensure it hasn’t been tampered with.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.