A Lambda function generates a 3 MB JSON file containing sensitive data and uploads it daily to S3. The developer must ensure the file is encrypted before uploading. Which change should the developer implement so the data is encrypted prior to the upload?

The correct approach is to call the GenerateDataKey API. This API returns a plaintext data key and an encrypted copy of that key. The Lambda function then uses the plaintext data key to encrypt the 3 MB JSON file before uploading it to S3. This ensures the data is encrypted client-side, fulfilling the requirement of encryption prior to upload. The encrypted data key is stored alongside the encrypted data in S3, allowing for decryption later. Using the default AWS KMS key for S3 or an S3-managed key (SSE-S3) encrypts the data at rest on S3 servers, not before upload. While these options encrypt the data, they don't meet the "prior to upload" requirement. Simply calling GenerateDataKey without using the returned key for client-side encryption wouldn't encrypt the file before it leaves the Lambda function.