This LFCS practice question tests your understanding of networking. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 financial firm requires all internal SSH connections to be encrypted with at least 256-bit ciphers. An administrator is configuring the SSH server. Which configuration line should be added to /etc/ssh/sshd_config?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "least"
Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
MACs hmac-sha2-256
Why wrong: MACs are for integrity, not encryption.
KexAlgorithms diffie-hellman-group-exchange-sha256
Why wrong: Key exchange algorithm, not encryption cipher.
Ciphers aes256-ctr
Specifies allowed ciphers; aes256-ctr is 256-bit.
HostKeyAlgorithms ssh-rsa
Why wrong: Host key algorithm, not encryption cipher.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Ciphers aes256-ctr
Option C is correct because the Ciphers directive in sshd_config explicitly controls the symmetric encryption algorithms used to encrypt SSH session data. The cipher aes256-ctr provides 256-bit encryption, meeting the firm's requirement for at least 256-bit ciphers. Other directives like MACs, KexAlgorithms, or HostKeyAlgorithms do not directly set the encryption cipher strength.
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.
MACs hmac-sha2-256
Why it's wrong here
MACs are for integrity, not encryption.
KexAlgorithms diffie-hellman-group-exchange-sha256
Why it's wrong here
Key exchange algorithm, not encryption cipher.
Ciphers aes256-ctr
Why this is correct
Specifies allowed ciphers; aes256-ctr is 256-bit.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
HostKeyAlgorithms ssh-rsa
Why it's wrong here
Host key algorithm, not encryption cipher.
Common exam traps
The trap here is that candidates confuse MACs, KexAlgorithms, or HostKeyAlgorithms with encryption ciphers, assuming any directive with '256' or 'sha256' implies 256-bit encryption, when only the Ciphers directive controls the symmetric encryption algorithm strength.
Detailed technical explanation
The Ciphers directive accepts a list of symmetric ciphers in order of preference; aes256-ctr is a 256-bit AES cipher in CTR (Counter) mode, which provides strong encryption and is widely supported. Under the hood, SSH negotiates the cipher during the key exchange phase, and the server's configured Ciphers list is matched against the client's offered ciphers. In a real-world scenario, if an administrator mistakenly sets only MACs or KexAlgorithms, the session might still use a weak cipher like aes128-cbc, failing compliance audits.
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 LFCS 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.
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FAQ
Networking — This question tests Networking — Read the scenario before looking for a memorised answer..
The correct answer is: Ciphers aes256-ctr — Option C is correct because the Ciphers directive in sshd_config explicitly controls the symmetric encryption algorithms used to encrypt SSH session data. The cipher aes256-ctr provides 256-bit encryption, meeting the firm's requirement for at least 256-bit ciphers. Other directives like MACs, KexAlgorithms, or HostKeyAlgorithms do not directly set the encryption cipher strength.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "least". You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This LFCS practice question is part of Courseiva's free Linux Foundation 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 LFCS exam.
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