In this example data can be read by the third party because the encryption key is entered while logged into the remote server. For my personal backup I ended up

In this example data can be read by the third party because the encryption key is entered while logged into the remote server. For my personal backup I ended up doing a daily rsync over ssh to a server in my house to an encrypted and compressed ZFS volume. This server then makes a daily snapshot and uses the ZFS send mechanism to transfer the snapshot incrementally to a third party OpenBSD ZFS VPS. This way the third party has no way of determining the key. It is done by shell scripts run with anacron on Debian systems. I can share the scripts if anybody is interested.