Unauthorized contents detection system

A data processing methodapplied to a data processing device including a verification key storage unit storing a verification key corresponding to a signature key;

• a using unit;
• a selecting unit;
• a calculating unit;
• a reading unit;
• a generating unit;
• a signature verifying unit;
• and a user control unit, and reading a digital work from a recording medium, the recording medium having recorded thereon the digital work;
• a plurality of record digest values generated from a plurality of data blocks constituting the digital work;
• record signature data generated by applying, with use of a signature key, a signature generating algorithm to a first combination made of some or all of the plurality of record digest values, the data processing method comprising:
• a using step of causing the using unit to play back the digital work;
• a selecting step of causing the selecting unit to, each time the digital work is played back, randomly select a predetermined number of data blocks from all of the plurality of data blocks, the predetermined number being smaller than the number of all of the plurality of data blocks;
• a calculating step of causing the calculating unit to calculate a plurality of calculation digest values from the selected data blocks;
• a reading step of causing the reading unit to read remaining record digest values corresponding to unselected data blocks from among the plurality of record digest values;
• a generating step of causing the generating unit to generate a second combination based on calculation digest values and the remaining record digest values, the second combination being the same as data which is generated from the first combination by replacing record digest values corresponding to the selected data blocks with corresponding calculation digest values;
• a signature verifying step of causing the signature verifying unit to verify the record signature data by applying, with use of the verification key, a signature verification algorithm to the second combination and the record signature data;
• and
• a use controlling step of causing the use controlling unit to stop the using unit from playing back the digital work when the verification is unsuccessful.

A data processing program applied to a data processing device including a verification key storage unit storing a verification key corresponding to a signature key;

• a using unit;
• a selecting unit;
• a calculating unit;
• a reading unit;
• a generating unit;
• a signature verifying unit;
• and a user control unit, and reading a digital work from a recording medium, the recording medium having recorded thereon the digital work;
• a plurality of record digest values generated from a plurality of data blocks constituting the digital work;
• record signature data generated by applying, with use of a signature key, a signature generating algorithm to a first combination made of some or all of the plurality of record digest values, the data processing program being recorded on another recording medium and causing the data processing device to execute:
• a using step of causing the using unit to play back the digital work;
• a selecting step of causing the selecting unit to, each time the digital work is played back, randomly select a predetermined number of data blocks from all of the plurality of data blocks the predetermined number being smaller than the number of all of the plurality of data blocks;
• a calculating step of causing the calculating unit to calculate a plurality of calculation digest values from the selected data blocks;
• a reading step of causing the reading unit to read remaining record digest values corresponding to unselected data blocks from among the plurality of record digest values;
• a generating step of causing the generating unit to generate a second combination based on calculation digest values and the remaining record digest values, the second combination being the same as data which is generated from the first combination by replacing record digest values corresponding to the selected data blocks with corresponding calculation digest values;
• a signature verifying step of causing the signature verifying unit to verify the record signature data by applying, with use of the verification key, a signature verification algorithm to the second combination and the record signature data;
• and
• a use controlling step of causing the use controlling unit to stop the using unit from playing back the digital work when the verification is unsuccessful.