Patent ID: 7743261
Filing Date: 2010-06-22
Classification: G06F,H04L,Y10S

Abstract:
1. A data processing device for playing back a digital work recorded on a recording medium having also recorded thereon (i) a plurality of record digest values generated from a plurality of data blocks constituting the digital work and (ii) 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 device comprising: a verification key storing unit configured to store a verification key corresponding to the signature key: a reading unit configured to read data recorded on the recording medium with use of a head radially movable on the recording medium; a using unit configured to playback the digital work; a selecting unit configured 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 the plurality of data blocks; an order determining unit configured to determine an order of reading the selected data blocks based on a current position of the head and a position, on the recording medium, where each of the selected data blocks is recorded; a first reading control unit configured to control said reading unit so as to read the selected data blocks according to the determined order; a calculating unit configured to calculate a predetermined number of calculation digest values from the selected data blocks, the calculated calculation digest values being equal to the selected data blocks in number; a second reading control unit configured to control said reading unit so as to read remaining record digest values corresponding to unselected data blocks from among the plurality of record digest values; a generating unit configured to generate a second combination based on the 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 unit configured 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 unit configured to stop the using unit from playing back the digital work when the verification is unsuccessful.