Patent ID: 7995766

Claim:
A group subordinate terminal in a key updating system that includes a server and a group of terminals including: a group managing terminal; and group subordinate terminals including said group subordinate terminal, said group subordinate terminal comprising: an apparatus-unique key holding unit configured to hold an apparatus-unique key that is a key corresponding to said group subordinate terminal only; a group key holding unit configured to hold a group key that is also held by the group managing terminal and the rest of the group subordinate terminals; an encryption and decryption processing unit configured to encrypt and decrypt data using either the apparatus-unique key or the group key; a group withdrawal request processing unit configured to transmit a group withdrawal request to the group managing terminal in response to an instruction to update the apparatus-unique key, the group withdrawal request requesting withdrawal of said group subordinate terminal from the group of terminals: an update apparatus-unique key requesting unit configured to request another apparatus-unique key by: receiving a group withdrawal certificate from the group managing terminal; and then transmitting the received group withdrawal certificate to the server, the group withdrawal certificate indicating that the withdrawal of said group subordinate terminal from the group of terminals is completed through invalidation of the group key; and an update processing unit configured to obtain the other apparatus-unique key from the server, and to rewrite the apparatus-unique key held by said apparatus-unique key holding unit to the obtained other apparatus-unique key, wherein said update processing unit is not allowed to obtain the other apparatus-unique key from the server until said update apparatus-unique key requesting unit transmits the received group withdrawal certificate to the server.