- A
Update the IAM policy to allow kms:Decrypt for all CMKs in the account using a wildcard resource (for example, arn:aws:kms:region:account-id:key/*).
Why wrong: This is not least privilege because it broadens access beyond the specific CMK used by the secret.
- B
Update the ECS task role IAM policy to grant kms:Decrypt on the CMK alias ARN (arn:aws:kms:region:account-id:alias/<alias-name>) or to include the new CMK ARN, so decrypt authorization matches the re-keyed CMK.
Since the IAM policy references only the old CMK ARN, it no longer matches the CMK used after re-keying. Using the alias ARN maintains least privilege and continues to work because the alias now points to the new CMK.
- C
Change the application to decrypt the secret itself using SSE-C keys so Secrets Manager no longer needs KMS.
Why wrong: Secrets Manager manages encryption at the service layer; the microservice still needs permission to allow Secrets Manager to decrypt using the CMK associated with the secret.
- D
Enable KMS key rotation for the old CMK so the CMK ARN resolves to the new key.
Why wrong: Key rotation affects the key material and versioning behavior, but it does not cause the old key ARN to become the new key ARN. The IAM resource mismatch remains.
SAA-C03 Design Secure Architectures Practice Question
This SAA-C03 practice question tests your understanding of design secure architectures. 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.
A microservice running in ECS retrieves a secret from AWS Secrets Manager. The secret is encrypted with a customer-managed CMK. An administrator re-keyed the secret to a new CMK (the key ARN changed), but kept the same KMS alias name. After re-keying, the service fails with an error from KMS: AccessDenied for kms:Decrypt. The ECS task role’s IAM policy still grants kms:Decrypt but only for the old CMK ARN. What is the best remediation to restore access while maintaining least privilege?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Update the ECS task role IAM policy to grant kms:Decrypt on the CMK alias ARN (arn:aws:kms:region:account-id:alias/<alias-name>) or to include the new CMK ARN, so decrypt authorization matches the re-keyed CMK.
Option B is correct because the ECS task role's IAM policy still references the old CMK ARN, but the secret is now encrypted with a new CMK. Since KMS authorization is based on the key ARN (not the alias), the policy must be updated to grant kms:Decrypt on the new CMK ARN or on the alias ARN (which resolves to the current underlying key). This restores access while maintaining least privilege by scoping permissions to the specific key used for 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.
- ✗
Update the IAM policy to allow kms:Decrypt for all CMKs in the account using a wildcard resource (for example, arn:aws:kms:region:account-id:key/*).
Why it's wrong here
This is not least privilege because it broadens access beyond the specific CMK used by the secret.
- ✓
Update the ECS task role IAM policy to grant kms:Decrypt on the CMK alias ARN (arn:aws:kms:region:account-id:alias/<alias-name>) or to include the new CMK ARN, so decrypt authorization matches the re-keyed CMK.
Why this is correct
Since the IAM policy references only the old CMK ARN, it no longer matches the CMK used after re-keying. Using the alias ARN maintains least privilege and continues to work because the alias now points to the new CMK.
Clue confirmation
The clue words "best", "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Change the application to decrypt the secret itself using SSE-C keys so Secrets Manager no longer needs KMS.
Why it's wrong here
Secrets Manager manages encryption at the service layer; the microservice still needs permission to allow Secrets Manager to decrypt using the CMK associated with the secret.
- ✗
Enable KMS key rotation for the old CMK so the CMK ARN resolves to the new key.
Why it's wrong here
Key rotation affects the key material and versioning behavior, but it does not cause the old key ARN to become the new key ARN. The IAM resource mismatch remains.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume KMS aliases can be used directly in IAM resource ARNs for authorization, but IAM policies that specify a key ARN (not an alias ARN) will fail after re-keying because the secret's encryption key has changed to a different CMK.
Detailed technical explanation
How to think about this question
KMS key aliases are mutable pointers that always resolve to the current underlying CMK, but IAM policies that specify a key ARN are static and do not follow alias changes. When a secret is re-keyed in Secrets Manager, the service re-encrypts the secret's ciphertext under the new CMK, so the old key ARN in the IAM policy no longer matches the key used for decryption. A real-world scenario is when an organization rotates CMKs for compliance; updating policies to use alias ARNs instead of key ARNs can reduce the need for policy changes during key rotation.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
Design Secure Architectures — This question tests Design Secure Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Update the ECS task role IAM policy to grant kms:Decrypt on the CMK alias ARN (arn:aws:kms:region:account-id:alias/<alias-name>) or to include the new CMK ARN, so decrypt authorization matches the re-keyed CMK. — Option B is correct because the ECS task role's IAM policy still references the old CMK ARN, but the secret is now encrypted with a new CMK. Since KMS authorization is based on the key ARN (not the alias), the policy must be updated to grant kms:Decrypt on the new CMK ARN or on the alias ARN (which resolves to the current underlying key). This restores access while maintaining least privilege by scoping permissions to the specific key used for decryption.
What should I do if I get this SAA-C03 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: "best", "least". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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