| 摘要 |
PROBLEM TO BE SOLVED: To appropriately conduct encryption in multicast communications. SOLUTION: A multicast server 2 encrypts a group session key Kgr, which is used in encryption of data for data service distribution, by a second encryption key Km, and transmits the encrypted key Kgr by unicast to a client who has subscribed to the service, out of clients belonging to a multicast group 3. When the client who has subscribed to the service receives the encrypted first encryption key transmitted by unicast, he/she decrypts it by a decryption key Km. Subsequently, the multicast server 2 encrypts data by the first encryption key, and transmits it by multicast to clients belonging to the multicast group 3. When clients receive encrypted data, they decrypt it by the first encryption key obtained from decrypting of the decryption key.
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