I've previously detailed howto use S3cmd to backup your data from a Linux machine. Unfortunately, because of the way that s3cmd works, if you want an incremental backup (i.e. using 'sync') you cannot use the built in encryption.
In this documentation I'll be detailing a simple way to implement an encrypted incremental backup using s3cmd, as well as a workaround if you're unable to install GPG - instead using OpenSSL to encrypt the data. Obviously we'll also be exploring how to decrypt the data when the backups are required
It's assumed that you've already got s3cmd installed and configured to access your S3 account (see my earlier documentation if not