PCNSE Decryption and SSL Inspection Practice Question
This PCNSE practice question tests your understanding of decryption and ssl inspection. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
During SSL decryption, the firewall logs show 'ssl_decrypt_unsupported_cipher' errors for several connections. What is the likely cause and solution?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The firewall's SSL/TLS service profile does not include the cipher suites used by the client or server.
The 'ssl_decrypt_unsupported_cipher' error indicates that the firewall's SSL/TLS proxy cannot negotiate a common cipher suite with the client or server during the decryption handshake. This occurs when the cipher suites configured in the firewall's SSL/TLS service profile do not include the ciphers offered by the client or required by the server. The solution is to update the service profile to include the necessary cipher suites, such as those based on AES-GCM or CHACHA20-POLY1305, ensuring compatibility.
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.
✓
The firewall's SSL/TLS service profile does not include the cipher suites used by the client or server.
Why this is correct
The cipher is unsupported; adding it to the profile resolves the issue.
Related concept
Read the scenario before looking for a memorised answer.
✗
The firewall does not support decryption of that traffic.
Why it's wrong here
It does support decryption but cannot handle the cipher.
✗
The decryption certificate is not trusted by the client.
Why it's wrong here
Trust errors produce certificate warnings, not cipher errors.
✗
The decryption rule is not matching the traffic.
Why it's wrong here
Matching issues would show no decryption, not cipher errors.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse cipher suite mismatch with certificate trust issues or rule misconfiguration, but the specific error message 'ssl_decrypt_unsupported_cipher' directly points to the cipher suite list in the SSL/TLS service profile.
Trap categories for this question
Command / output trap
Matching issues would show no decryption, not cipher errors.
Detailed technical explanation
How to think about this question
The firewall acts as a TLS proxy, performing a full handshake with both client and server. During the ServerHello, the firewall selects a cipher suite from its configured profile; if none of the client-offered ciphers are in the profile, the handshake fails with an 'unsupported_cipher' alert (RFC 5246). A common real-world scenario is when a legacy server requires a cipher like TLS_RSA_WITH_3DES_EDE_CBC_SHA, which is often excluded from modern profiles due to security policies, causing this error.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation 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.
Decryption and SSL Inspection — This question tests Decryption and SSL Inspection — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The firewall's SSL/TLS service profile does not include the cipher suites used by the client or server. — The 'ssl_decrypt_unsupported_cipher' error indicates that the firewall's SSL/TLS proxy cannot negotiate a common cipher suite with the client or server during the decryption handshake. This occurs when the cipher suites configured in the firewall's SSL/TLS service profile do not include the ciphers offered by the client or required by the server. The solution is to update the service profile to include the necessary cipher suites, such as those based on AES-GCM or CHACHA20-POLY1305, ensuring compatibility.
What should I do if I get this PCNSE 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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Question Discussion
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