Access control system and method based on hierarchical key, and authentication key exchange method thereof

Disclosed relates to an access control system and method based on hierarchical keys. The system comprises an access control server (ACS), a home gateway, and a plurality of sensor devices disposed on a home network. The ACS sets up user's access limits of authority and authorization verifier, and saves the related data of user's password and the user's access limits of authority. The gateway records the authority limits' level and the authority limits' key which are constructed based on a hierarchical key structure. When a user logs in the ACS to request access, an one-time communication key between the user and the home gateway is established by exchanging the ticket and the token that are issued by the ACS. This allows the user to access the information of the sensor devices.