DATA DECODING DEVICE, ATTRIBUTE-BASED ENCRYPTION SYSTEM, RANDOM NUMBER ELEMENT REMOVING DEVICE, RANDOMIZED SECRET KEY GENERATION DEVICE, DATA DECODING METHOD, AND DATA DECODING PROGRAM

摘要

The purpose of the present invention is to enhance the security of encoded data by executing attribute-based encryption-type decoding processing stage by stage, the processing being divided into a plurality of stages. A KEM key part decoding section (320) decodes an encoded KEM key (313) that is a common key encoded by using an attribute condition expression, by using an r-user secret key (221) that is obtained by including a random number element in a user secret key generated by an attribute-based encryption method, thereby to generate an r-KEM key mask value (321) that includes a random number element. A random number element removal request section (330) requests an IC card (400) to remove the random number element from the r-KEM key mask value (321), and obtains a KEM key mask value (411) from the IC card (400). A mask removal section (340) generates a KEM key (341) by using the KEM key mask value (411). A data decoding section (350) obtains target data (301) by decoding encoded data main body (312), by using the KEM key (341).