Patent ID: 8261084
Filing Date: 2012-09-04
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, comprising: a verification key storing unit operable to store a verification key corresponding to the signature key; a using unit operable to play back the digital work; a judging unit operable to judge whether or not verification of the digital work should be performed; a selecting unit operable to, each time the digital work is played back, randomly select a predetermined number of data blocks from the plurality of data blocks, the predetermined number being smaller than the number of all the plurality of data blocks; a calculating unit operable to calculate a plurality of calculation digest values from the selected data blocks; a reading unit operable to read at least remaining record digest values corresponding to unselected data blocks from among the plurality of record digest values; a generating unit operable 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 operable to perform a signature verification 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 operable to stop the playback of the digital work when the signature verification performed by the signature verifying unit is unsuccessful, wherein the signature verifying unit performs the signature verification, when the judging unit has judged that the verification of the digital work should be performed.