With Server Side Encryption, Amazon handles the encryption and decryption of data stored in S3. With the service, users can encrypt data by adding an additional request header when writing the object to S3, Amazon said. When users download the objects, decryption occurs automatically.
Amazon touts its S3 encryption service as freeing users from the work of managing encryption keys. The alternative is for users to encrypt data on their side and upload the encrypted data to Amazon S3.
Enterprises should stick with client-side encryption, in most cases, according to Rich Mogull, founder of Securosis LLC., an independent security consulting firm.
“The only thing that server side like this helps with is concerns over physical loss of the drives the data is stored on,” he said in an email. “Amazon already has very good policies around protecting those drives, so I don't see the advantages for server side.”
The Amazon S3 Server Side Encryption uses the 256-bit Advanced Encryption Standard.