KEY INFORMATION CONTROL DEVICE, KEY INFORMATION UPDATING DEVICE, PROGRAM AND RECORDING MEDIUM, KEY INFORMATION UPDATING METHOD, AND KEY INFORMATION UPDATING SYSTEM

摘要

Provided are a key information control device, etc., with which communication is possible even if a group key update has failed. Group keys (K(Gn)) that are used in a network including a key information control device (1) and a plurality of communication devices (2A, 2B, 2C) are updated. New group keys (K(G1), K(G2), K(G3)) are transmitted from the key information control device (1) by multicast communication, and the group keys of the communication devices (2A, 2B, 2C) are updated to the group keys (K(Gn)) transmitted from the key information control device (1). The EPOCH value, which is a value in the information transmitted from the communication devices (2A, 2B, 2C) that is updated each time the group key is updated, is checked, and if a communication device (2A) that has not received the updated group key (K(G3)) is detected, a key update message is transmitted to the communication device (2A) by unicast communication that has a retransmission function.