ENCRYPTED COMMUNICATION SYSTEM, KEY DELIVERY SERVER THEREOF, TERMINAL DEVICE, AND KEY SHARING METHOD

摘要

A method for providing a highly-safe and high-speed group key updating method. The method includes a step of executing a part of decoding processing for decoding an encrypted group key used for information decoding in a subscriber terminal before delivery of the group key, a step of delivering the group key and individual decoding information for each terminal device for executing a part of the remaining part of the decoding processing of the group key, and a step of executing in the subscriber terminal a group key decoding processing using the delivered decoding information and the result of the part of the decoding processing executed in advance