Which solution meets these requirements?
Use client-side encryption to encrypt the data that is being uploaded to the S3 buckets.
Use server-side encryption to encrypt the data that is being uploaded to the S3 buckets.
Create bucket policies that require the use of server-side encryption with S3 managed encryption keys (SSE-S3) for S3 uploads.
Enable the security option to encrypt the S3 buckets through the use of a default AWS Key Management Service (AWS KMS) key.
Explanations:
Client-side encryption ensures that data is encrypted before it is sent to S3, thus securing the data at rest and in transit. This method gives full control over the encryption keys to the client, ensuring that the data remains protected throughout the upload process.
Server-side encryption (SSE) encrypts data at rest within S3, but it does not provide encryption in transit unless combined with HTTPS. Thus, it does not fully meet the requirement for both at rest and in transit encryption by itself.
While creating bucket policies to require server-side encryption with SSE-S3 can enforce encryption at rest, it does not address encryption in transit. Without specific measures taken for in-transit encryption, this option alone is insufficient.
Enabling the default AWS KMS key for S3 buckets provides server-side encryption at rest but does not inherently ensure encryption in transit. Therefore, this option does not fully satisfy both requirements of the problem.
As I recall, the answer is:
Use client-side encryption to encrypt the data that is being uploaded to the S3 buckets.