Which solution will meet this requirement?
Create an AWS Key Management Service (AWS KMS) key. Assign the KMS key to the S3 bucket.
Set the x-amz-server-side-encryption header when invoking the PutObject API operation.
Provide the encryption key in the HTTP header of every request.
Apply TLS to encrypt the traffic to the S3 bucket.
Explanations:
Creating an AWS KMS key and assigning it to the S3 bucket enables server-side encryption with KMS-managed keys (SSE-KMS), not with S3-managed keys (SSE-S3). SSE-S3 does not require a KMS key.
Setting thex-amz-server-side-encryptionheader toAES256when invoking the PutObject API operation specifies that the object should be encrypted at rest using server-side encryption with Amazon S3 managed keys (SSE-S3). This is the correct method to ensure SSE-S3 is applied.
Providing the encryption key in the HTTP header is not a valid approach for SSE-S3. SSE-S3 does not require explicit encryption keys as it uses S3-managed keys automatically for encryption at rest.
Applying TLS encrypts data in transit but does not affect how data is stored at rest in S3. This option does not address the requirement of encrypting objects at rest with SSE-S3.
In my opinion, the answer is:
Set the x-amz-server-side-encryption header when invoking the PutObject API operation.