End-to-end encryption means neither Dropbox nor Ensafer can access your files. Your files are encrypted before they leave your computer, and never decrypted before they arrive at one of your other devices. This means anyone gaining access to the files in-between are unable to view the content of the files.
Your encryption keys are also encrypted before they leave your computer, and can not be opened by Ensafer or any third party, even with access to the Ensafer servers. When you share files, separate key pairs are used, so anyone gaining access to these keys will not gain access to your personal files.
We take your privacy seriously, like it should.