Files are each encrypted with their own, unique key, which is stored in the metadata file. All data in the metadata file is, in turn, securely encrypted and files names and directory structures are also hidden from the server using a unique UUID as name for each file.
When enable encryption you will get an unique password(12 characters).You need the password to open encrypted files on other devices
Encryption works at folder level.To enable encryption you need to flag an empty folder.(It's impossible to access encrypted files through web interface.)