| 摘要 |
Content is transmitted within a range of the user's legitimate use while limiting the number of equipment to which the content is transmitted at the same time. A content using apparatus periodically transmits an exchange key and the corresponding key ID using a command. Only while receiving the key ID at predetermined reception cycles, a content providing apparatus maintains the corresponding exchange key. When not periodically receiving the key ID, the content providing apparatus destroys the corresponding exchange key. After that, when receiving a command including the key ID, the content providing apparatus returns a response including information indicating that the exchange key has become invalid.
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