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Communication and Network Security →mediumMultiple ChoiceObjective-mapped

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 wants to secure email communications for its employees. They need to ensure message confidentiality and integrity, and also verify the sender's identity. Which protocol uses a hierarchical public key infrastructure (PKI) for email encryption and signing?

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

✓

S/MIME

S/MIME (Secure/Multipurpose Internet Mail Extensions) is the correct answer because it is specifically designed to provide email encryption and digital signing using a hierarchical public key infrastructure (PKI) based on X.509 certificates. This allows the company to ensure message confidentiality (via encryption), integrity (via hashing and signing), and sender authentication (via certificate validation against a trusted root CA).

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.

  • ✓

    S/MIME

    Why this is correct

    S/MIME relies on X.509 certificates issued by CAs, forming a hierarchical PKI.

    Related concept

    Read the scenario before looking for a memorised answer.

  • ✗

    PGP

    Why it's wrong here

    PGP uses a web of trust, not a hierarchical PKI.

  • ✗

    TLS

    Why it's wrong here

    TLS secures web traffic, not email specifically (though it can secure SMTP).

  • ✗

    SSH

    Why it's wrong here

    SSH secures remote shell access, not email.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is confusing PGP's Web of Trust with S/MIME's hierarchical PKI, as both can encrypt and sign emails, but only S/MIME relies on a formal CA hierarchy as described in the question.

Detailed technical explanation

How to think about this question

S/MIME leverages X.509 v3 certificates issued by a Certificate Authority (CA) in a hierarchical PKI, where each certificate chains up to a trusted root. The encryption uses a hybrid approach: a random session key (e.g., AES-256) encrypts the message, and the session key is then encrypted with the recipient's RSA or ECDH public key. Digital signatures are created by hashing the message (e.g., SHA-256) and signing the hash with the sender's private key, allowing recipients to verify the signature using the sender's public certificate.

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.

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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: S/MIME — S/MIME (Secure/Multipurpose Internet Mail Extensions) is the correct answer because it is specifically designed to provide email encryption and digital signing using a hierarchical public key infrastructure (PKI) based on X.509 certificates. This allows the company to ensure message confidentiality (via encryption), integrity (via hashing and signing), and sender authentication (via certificate validation against a trusted root CA).

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

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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.