The correct Config rule for finding buckets that are not usingSSE-KMS by defaultiss3-default-encryption-kms. It evaluates the bucket’s default encryption settings and flags buckets that do not have KMS default encryption enabled. The s3-bucket-ssl-requests-only rule focuses on enforcing HTTPS-only requests and does not validate encryption-at-rest settings, so it cannot satisfy the “identify not encrypted with KMS” requirement.

For preventing uploads of objects that are not encrypted with KMS, an organization-wide control is needed. AnSCPcan restrict s3:PutObject so that uploads succeed only when the request specifiesSSE-KMS(and optionally a specific KMS key). This provides broad, low-touch enforcement across many accounts and buckets. While bucket policies can also enforce SSE-KMS, managing and verifying hundreds of bucket policies is more operationally heavy than a centrally managed SCP guardrail.

Option B enforcesSSE-S3, which does not meet the requirement forKMSencryption. Option D uses the wrong Config rule and relies on an “allow-only” pattern rather than explicit deny logic, making it an unreliable fit for the stated goal. Therefore, A is the best answer.