Patent ID: 8077865

Claim:
An electronic device comprising: a storage unit storing right information used for managing whether or not a content can be played back, the right information being stored in a state protected from unauthorized accesses; a receiving unit including a microprocessor operable to receive, one by one, a plurality of frames that constitute the content in an encrypted state; a right judging unit including a microprocessor operable to judge whether or not the content is permitted to be played back, in accordance with the right information; a control unit including a microprocessor operable to (a) cause the right judging unit to perform the judgment each time an Nth frame, of the plurality of frames, is received by the receiving unit and a value N satisfies a predetermined judgment condition, the value N being a natural number indicating a position of a frame in an order of a playback of the plurality of frames constituting the content, (b) decrypt the Nth frame and cause the decrypted Nth frame to be played back, when the right judging unit judges that the content is permitted to be played back, and (c) restrict the playback of frames, of the plurality of frames, located after the Nth frame, when the right judging unit judges that the content is not permitted to be played back; and a tamper detection unit including a microprocessor operable to perform a tamper detection for a part of an application module that plays back the content, and each time a tamper is detected, sequentially change the part of the application module for which the tamper detection is to be performed, wherein the tamper detection unit performs the tamper detection for a first part of the application module when a value indicating a position of a currently received frame, of the plurality of frames received by the receiving unit, satisfies the predetermined judgment condition a first time, and performs the tamper detection for a second part, which is different from the first part, of the application module when the value indicating the position of the currently received frame, of the plurality of frames received by the receiving unit, satisfies the predetermined judgment condition a second time.