The correct answer is the "Block sessions with untrusted issuers" setting. When the firewall performs SSL decryption, it intercepts the server's certificate and re-signs it using its own internal CA. If the original server certificate was issued by a CA that the firewall does not recognize as trusted, the firewall cannot validate the certificate chain, and if this block setting is enabled, it will drop the session with a decryption error. On the PCNSA exam, this question tests your understanding of how SSL Forward Proxy decryption handles certificate validation failures, a common pitfall when enabling decryption without first importing necessary public CA certificates. A frequent trap is confusing this with certificate revocation checks or SSL protocol versions. Remember the key distinction: untrusted issuer means the firewall does not know the root CA, not that the certificate is expired or revoked. Memory tip: "If the issuer is a stranger, block the danger."
PCNSA Decryption and Monitoring Practice Question
This PCNSA practice question tests your understanding of decryption and monitoring. 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.
After enabling SSL decryption, users report that some websites fail to load. The firewall logs show 'decryption error' for these sites. Which decryption profile setting should the administrator check first?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Block sessions with untrusted issuers
When SSL decryption is enabled, the firewall acts as a man-in-the-middle and must re-sign the server's certificate with its own CA. If the server's certificate is issued by an untrusted CA (i.e., not in the firewall's trusted CA list), the firewall cannot verify the chain of trust and will block the session if the 'Block sessions with untrusted issuers' option is enabled. This is the most common cause of 'decryption error' logs for sites that previously worked without decryption.
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.
✗
Block sessions with expired certificates
Why it's wrong here
Expired certificates also cause errors, but untrusted issuers are a more common first check.
✗
Block sessions with certificate status unknown
Why it's wrong here
This setting depends on CRL/OCSP; it is less likely to be the first cause.
✗
Block sessions with unsupported cipher suites
Why it's wrong here
Unsupported ciphers cause a different failure, not typically logged as 'decryption error'.
✓
Block sessions with untrusted issuers
Why this is correct
If enabled, sessions with certificates from untrusted CAs will be blocked, causing 'decryption error'.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'untrusted issuer' with 'expired certificate' or 'certificate status unknown', but the 'decryption error' log specifically points to a chain-of-trust validation failure, which is directly controlled by the 'Block sessions with untrusted issuers' setting.
Detailed technical explanation
How to think about this question
Under the hood, the firewall's SSL forward proxy decrypts traffic by generating a new certificate on-the-fly signed by its internal CA. If the original server certificate's issuer is not in the firewall's trusted CA store (e.g., a private or self-signed CA), the firewall cannot validate the chain and will treat it as untrusted. In real-world scenarios, this often occurs with internal applications using enterprise CAs that are not imported into the firewall, or with sites using Let's Encrypt certificates if the firewall's CA bundle is outdated.
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 practitioner preparing for the PCNSA 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
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 Monitoring — This question tests Decryption and Monitoring — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Block sessions with untrusted issuers — When SSL decryption is enabled, the firewall acts as a man-in-the-middle and must re-sign the server's certificate with its own CA. If the server's certificate is issued by an untrusted CA (i.e., not in the firewall's trusted CA list), the firewall cannot verify the chain of trust and will block the session if the 'Block sessions with untrusted issuers' option is enabled. This is the most common cause of 'decryption error' logs for sites that previously worked without decryption.
What should I do if I get this PCNSA question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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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