Information processing system and method

An information processing method for use in a system in which a key tree is formed so as to include leaves, a root, and nodes existing in paths from the respective leaves to the root;

• a plurality of devices are assigned to respective leaves;
• keys are assigned to the root, the leaves, and the nodes, located in paths from the root to leaves;
• an enabling key block (EKB) is produced which includes data produced by selecting a path in the key tree and encrypting an upper-level key in the selected path using a lower-level key in the selected path such that the encrypted data can be decrypted only by the device which can use a node key set corresponding to the selected path;
• and the resultant enabling key block (EKB) is provided to the device,
• wherein a key distribution center (KDC), which produces and issues an EKB capable of being decrypted in common in one or more category trees, sends a notification of a change in state of a category tree capable of processing an EKB identified in the EKB type definition list, in which the correspondence between an EKB type identifier and one or more identification data identifying one or more category trees capable of processing an EKB of an EKB type identified by the EKB type identifier is described, to at least an entity that uses the EKB capable of being processed in the category tree in which the change in state has occurred.

A program storage medium having a computer program stored therein for causing a computer system to execute information processing in an information processing system in which a key tree is formed so as to include leaves, a root, and nodes existing in paths from the respective leaves to the root;

• a plurality of devices are assigned to respective leaves;
• keys are assigned to the root, the leaves, and the nodes, located in paths from the root to leaves;
• an enabling key block (EKB) is produced which includes data produced by selecting a path in the key tree and encrypting an upper-level key in the selected path using a lower-level key in the selected path such that the encrypted data can be decrypted only by the device which can use a node key set corresponding to the selected path;
• and the resultant enabling key block (EKB) is provided to the device, the computer program comprising the steps of:
• receiving state change information indicating occurrence of a change in state of a category tree from a category entity that manages said category tree;
• and
• producing a notification of the change in state in accordance with the state change information received from the category entity and sending the produced notification to at least an entity that uses the EKB capable of being processed in the category tree in which the change in state has occurred.