| 摘要 |
Content is transmitted in an appropriate usage range for a user while the number of devices simultaneously transmitting content is limited. A content usage device periodically transmits, by means of a command, a key ID which corresponds to an exchange key. A content provision device holds the corresponding exchange key only for as long as the key ID can be received in each specified reception period. The content provision device discards the corresponding exchange key when the key ID can no longer be periodically received. Thereafter, when a command including the key ID is received, a response including information indicating that the exchange key is invalid is returned. |
