| 摘要 |
A system in which content usage conditions can be upgraded without the need for a service provider to control content-usage rights of a user. In the system in which encrypted content is distributed and is allowed to be utilized only by authorized users, the service provider receives a content usage-right certificate from the user, and on the condition that it is determined that data is not tampered with by verifying a digital signature of an issuing entity of the content usage-right certificate, the service provider obtains user information and content purchase information of the user from the content usage-right certificate, and performs upgrade processing by, for example, changing the usage conditions. It is thus possible to change the content usage conditions without the need for the service provider to possess usage control data. |
