A company stores log data from multiple accounts in centralized Amazon S3 buckets. A solutions architect must ensure the data is encrypted at rest before upload to S3 and encrypted in transit. Which solution meets these requirements?

The correct answer is to use client-side encryption. This ensures data is encrypted before being uploaded to S3, satisfying the "encrypted at rest before upload" requirement. Client-side encryption also inherently provides encryption in transit because the data is already encrypted before it leaves the client. Server-side encryption (SSE-S3, SSE-KMS, SSE-C) encrypts data after it arrives at S3. While it encrypts data at rest within S3 and can use HTTPS for in-transit encryption, it does not encrypt the data before the upload process begins from the client's perspective. Therefore, options involving server-side encryption or bucket policies requiring it do not meet the "before upload" criterion for at-rest encryption.