The user nobody find itself on a Linux system, looks around and finds a directory /backup with a tar archive that contains /etc, /home, and /root.
So it also contains the .ssh directory of user felix and a ssh key that is not password protected.
Extracting the key to /tmp user nobody logs in as user felix.
When creating the backup the umask value was the default 022 so the file permissions result -rw-r–r–.
Since the backup is created with root permissions nobody can extract and access EVERYTHING