Quick Answer
The answer is 600. This permission setting ensures that the private key file is readable and writable only by its owner, typically root or the dedicated application user, which is essential because private keys must never be exposed to other users or processes on the system. On Linux, permission 600 translates to owner read and write (rw-------), blocking all access for group members and others, thereby preventing unauthorized reading or modification of the key. On the CompTIA SecurityX CAS-004 exam, this concept tests your understanding of least privilege and file system security controls, often appearing in scenario-based questions about securing TLS or SSH configurations. A common trap is confusing 600 with 644 or 755, which grant world-readable access and would immediately fail a security audit. To remember, think of the private key as a secret that only one person should hold: the owner gets full control (6), and everyone else gets nothing (00).
This CAS-004 practice question tests your understanding of application environment, configuration and security. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 system administrator is configuring a Linux server to host a web application. Which file permission should be set for the private SSL key?
600
600 grants read/write to owner only, which is secure for private keys.
644
Why wrong: 644 allows read access to group and others, exposing the key.
444
Why wrong: 444 allows read-only to everyone, exposing the key to all users.
755
Why wrong: 755 allows read/execute to group and others, inappropriate for a private key.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
600
Private keys must be readable only by the owner (usually root or the application user). Permission 600 ensures only the owner can read and write the file, preventing unauthorized access.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
600
Why this is correct
600 grants read/write to owner only, which is secure for private keys.
Related concept
Read the scenario before looking for a memorised answer.
644
Why it's wrong here
644 allows read access to group and others, exposing the key.
444
Why it's wrong here
444 allows read-only to everyone, exposing the key to all users.
755
Why it's wrong here
755 allows read/execute to group and others, inappropriate for a private key.
Common exam traps
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the CAS-004 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Identify which CAS-004 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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FAQ
Application Environment, Configuration and Security — This question tests Application Environment, Configuration and Security — Read the scenario before looking for a memorised answer..
The correct answer is: 600 — Private keys must be readable only by the owner (usually root or the application user). Permission 600 ensures only the owner can read and write the file, preventing unauthorized access.
Identify which CAS-004 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This CAS-004 practice question is part of Courseiva's free CompTIA 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 CAS-004 exam.
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