My current task is to set up a (remote) backup (using rsync/rsnapshot) over sftp of /home (linux). Obviously some files are read only for the owner (ie -r-------; and should stay that way) so i guess I'll need the root user to back up those files. Setting up an rsync daemon seems also too insecure to me.
However, I do hesitate to use an ssh key for that purpose due to security concerns (if the backup server get's owned the attacker will have direct shells to other servers). I was thinking of creating a backup user with chroot sftp (as suggested Chroot SFTP - Possible to allow user to write to current (chroot) directory) but I guess I'd cripple my root user as I would loose shell access :(.
What setup would you suggest?