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
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.
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.
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
TLS 1.3 intentionally removes backward compatibility with older, insecure protocols like SSL 3.0. This decision was made to eliminate known vulnerabilities, such as the POODLE attack, which exploited weaknesses in SSL 3.0's padding oracle. By dropping support for deprecated versions, TLS 1.3 ensures that connections cannot downgrade to less secure cryptographic standards, thereby enforcing a higher baseline security posture and protecting against known exploits.
- ✗
Use of RSA key exchange for authentication
Why it's wrong here
TLS 1.3 explicitly removes support for static RSA key exchange mechanisms. This removal is a critical step towards mandating forward secrecy, as static RSA key exchange does not provide this essential property. If a server's long-term private RSA key were compromised, all past communications encrypted with keys derived from that static exchange could be retroactively decrypted, a risk TLS 1.3 mitigates by prioritizing ephemeral key exchanges.
- ✗
Support for RC4 stream cipher
Why it's wrong here
The RC4 stream cipher is explicitly prohibited and removed from TLS 1.3's suite of supported algorithms. RC4 has known cryptographic weaknesses, including biases in its keystream generation, which can lead to recovery of plaintext data through statistical analysis after a sufficient number of encrypted messages. Its removal is part of TLS 1.3's broader effort to eliminate all known weak or compromised cryptographic primitives, ensuring only robust algorithms are used.
- ✓
Mandatory forward secrecy via ephemeral Diffie-Hellman
Why this is correct
TLS 1.3 mandates forward secrecy, primarily achieved through the exclusive use of ephemeral Diffie-Hellman (DHE or ECDHE) key exchange mechanisms. This means that a unique, temporary session key is generated for each connection, which is then discarded after the session ends. Even if a server's long-term private key is compromised in the future, past session keys cannot be derived, thus protecting the confidentiality of previously recorded communications. This design significantly enhances long-term data security against future compromises.
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
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.
Key term
Security
Security in IT is the practice of protecting systems, networks, and data from unauthorized access, damage, or theft.
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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.