Patent ID: 8972737
Filing Date: 2015-03-03
Classification: G06F,H04L,Y10S

Abstract:
1. A data processing device for using 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 at least some or all of the plurality of record digest values, the data processing device comprising: a hardware processor; and a non-transitory memory storing therein a program which when executed by the hardware processor causes the data processing device to operate as the following units: a reading unit configured to read data recorded on the recording medium with use of a head radially movable on the recording medium; a verification key storing unit configured to store a verification key corresponding to the signature key; a using unit configured to use the digital work; a selecting unit configured to, each time the digital work is used, 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 (i) a position of the head when the head is located closest to an inner circumference of the recording medium and (ii) a position, on the recording medium, where each of the selected data blocks is recorded; a reading control unit configured to control the reading unit so as to read the selected data blocks according to the determined order; and a calculating unit configured to calculate a plurality of calculation digest values from the selected data blocks, wherein the reading unit further reads remaining record digest values corresponding to unselected data blocks from among the plurality of record digest values, and the data processing device further comprises 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, and 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.