SCS-C02 kms:ViaService Practice Question
A company uses AWS KMS to encrypt objects in an S3 bucket. The security team wants to ensure that only users with the appropriate KMS key permissions can decrypt objects. Which TWO conditions should be included in the S3 bucket policy to enforce this? (Choose TWO.)
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
✓
"Condition": {"StringEquals": {"kms:ViaService": "s3.us-east-1.amazonaws.com"}}
Options A and E are the only distinct conditions that can be used in an S3 bucket policy to enforce that only users with appropriate KMS key permissions can decrypt objects. kms:ViaService restricts the use of the KMS key to requests coming via the S3 service, and kms:EncryptionContext restricts decryption to requests that include the specific S3 bucket ARN. Option C is identical to A and thus does not provide an additional constraint, making it redundant. Options B and D are not valid condition keys for S3 bucket policies.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
"Condition": {"StringEquals": {"kms:ViaService": "s3.us-east-1.amazonaws.com"}}
Why this is correct
Correct. This condition restricts the KMS key to be used only via the S3 service, ensuring that decryption requests must come through S3.
- ✗
"Condition": {"StringEquals": {"kms:KeySpec": "SYMMETRIC_DEFAULT"}}
Why it's wrong here
Incorrect. kms:KeySpec is not a valid condition key in S3 bucket policies; it is used in KMS key policies or IAM policies for KMS API calls.
- ✗
"Condition": {"StringEquals": {"kms:ViaService": "s3.us-east-1.amazonaws.com"}}
Why it's wrong here
Incorrect. This condition is identical to A, so it does not provide a distinct constraint. Selecting both A and C would not satisfy the requirement for three distinct conditions.
- ✗
"Condition": {"StringEquals": {"kms:GranteePrincipal": "arn:aws:iam::123456789012:role/Admin"}}
Why it's wrong here
Incorrect. kms:GranteePrincipal is used in KMS grants, not in S3 bucket policies.
- ✓
"Condition": {"StringEquals": {"kms:EncryptionContext": {"aws:s3:arn": "arn:aws:s3:::my-bucket"}}}
Why this is correct
Correct. This condition uses kms:EncryptionContext to match the specific S3 bucket ARN, ensuring that decryption is allowed only for that bucket.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SCS-C02 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 SCS-C02 exam.