Communications apparatus, communications system, and method of setting certificate

A system which includes at least a high-level apparatus and a plurality of low-level apparatuses, at least one of the low-level apparatuses comprising:

• a storage unit configured to store an individual certificate set and a common certificate set,
• wherein the common certificate set is the same common certificate set stored in advance on the other of the plurality of low-level apparatuses, said common certificate set being used for storing a new individual certificate set in the low-level apparatus, and
• wherein the individual certificate set is configured to include own authentication information and an individual root-key certificate, the own authentication information including information uniquely identifying the apparatus, the individual root key certificate being the same for the other of the plurality of low-level apparatuses and is used to authenticate the validity of the high level apparatus;
• and
• a communication unit configured to transmit the own authentication information to the high level apparatus to allow the high level apparatus to perform decryption to authenticate the validity of the low-level apparatus.

A method of communicating implemented on an apparatus in a system which includes at least a high-level apparatus and a plurality of low-level apparatuses, said apparatus being one of the low-level apparatuses, the method comprising:

• storing, at the apparatus, an individual certificate set and a common certificate set,
• wherein the common certificate set is the same common certificate set stored in advance on the other of the plurality of low-level apparatuses, said common certificate set being used for storing a new individual certificate set in the apparatus, and
• wherein the individual certificate set is configured to include own authentication information and an individual root-key certificate, the own authentication information including information uniquely identifying the apparatus, the individual root key certificate being the same for the other of the plurality of low-level apparatuses and is used to authenticate the validity of the high level apparatus;
• and
• transmitting, at the apparatus, the own authentication information to the high level apparatus to allow the high level apparatus to perform decryption to authenticate the validity of the apparatus.