Quick Answer
The answer is the `kms:Decrypt` permission. This is required in the CloudTrail S3 bucket policy because CloudTrail must first decrypt the bucket’s AWS KMS key to verify the integrity of any existing encrypted objects before it can write new log data. While `kms:Encrypt` is needed on the object itself, the bucket policy must explicitly grant `kms:Decrypt` for the key to allow CloudTrail to perform this verification step. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your understanding of the subtle distinction between key-level and object-level permissions in a KMS-encrypted logging setup. A common trap is assuming CloudTrail only needs `kms:Encrypt` to write logs, but the service actually performs a decrypt check first. Remember the memory tip: "Decrypt to verify, Encrypt to store"—the bucket policy must include `kms:Decrypt` for the key, while the object-level permission handles the encryption.
This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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 security engineer is configuring AWS CloudTrail to log all management events across all regions. The logs must be stored in an S3 bucket that is encrypted with an AWS KMS key. Which bucket policy element is required to allow CloudTrail to write logs?
kms:Encrypt
Why wrong: Encrypt is needed, but Decrypt is also required for the bucket policy.
kms:GenerateDataKey
Why wrong: CloudTrail uses server-side encryption with KMS, not GenerateDataKey.
kms:CreateKey
Why wrong: CloudTrail does not create KMS keys; it uses existing ones.
kms:Decrypt
CloudTrail needs decrypt permission to verify the key before encrypting logs.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
kms:Decrypt
Option B is correct because CloudTrail requires the kms:Decrypt permission for the bucket key to verify encrypted objects. Option A is wrong because CloudTrail does not need kms:CreateKey. Option C is wrong because kms:Encrypt is needed for the object, but the bucket policy must include Decrypt for the key. Option D is wrong because kms:GenerateDataKey is not used by CloudTrail.
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.
kms:Encrypt
Why it's wrong here
Encrypt is needed, but Decrypt is also required for the bucket policy.
kms:GenerateDataKey
Why it's wrong here
CloudTrail uses server-side encryption with KMS, not GenerateDataKey.
kms:CreateKey
Why it's wrong here
CloudTrail does not create KMS keys; it uses existing ones.
kms:Decrypt
Why this is correct
CloudTrail needs decrypt permission to verify the key before encrypting logs.
Related concept
Read the scenario before looking for a memorised answer.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Identify which ANS-C01 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
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — Read the scenario before looking for a memorised answer..
The correct answer is: kms:Decrypt — Option B is correct because CloudTrail requires the kms:Decrypt permission for the bucket key to verify encrypted objects. Option A is wrong because CloudTrail does not need kms:CreateKey. Option C is wrong because kms:Encrypt is needed for the object, but the bucket policy must include Decrypt for the key. Option D is wrong because kms:GenerateDataKey is not used by CloudTrail.
Identify which ANS-C01 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 20, 2026
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services 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 ANS-C01 exam.
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