If the Black Box device selected to be the server will only have one client device, then the authorized_keys file is simply a copy of the public key for
that device. If one or more devices will be clients of the server, then the authorized_keys file will contain a copy of all of the public keys. RSA and
DSA keys may be freely mixed in the authorized_keys file. For example, assume we already have one server, called bridge_server, and two sets of
keys, for the control_room and the plant_entrance:
$ ls /home/user/keys control_room control_room.pub plant_entrance plant_entrance.pub $ cat /home/user/keys/control_room.pub