DATA DECRYPTION DEVICE, ATTRIBUTE-BASED ENCRYPTION SYSTEM, RANDOM NUMBER ELEMENT REMOVING DEVICE, DATA DECRYPTION METHOD, AND DATA DECRYPTION PROGRAMM.

摘要

The object is to enhance the security of encrypted data by dividing a decrypting process of an attribute-based encryption scheme into a plurality of stages and executing the decrypting process. A KEM key partly decrypting part 320 generates an r-KEM key mask value 321 including a random number element, by performing a decrypting process for an encrypted KEM key 313 being a common key encrypted using an attribute conditional expression, using an r-user secret key 221 which is obtained by including the random number element into a user secret key generated in accordance with the attribute-based encryption scheme. A random number element removal requesting part 330 requests an IC card 400 to remove the random number element from the r-KEM key mask value 321, and acquires a KEM key mask value 411 from the IC card 400. A mask removing part 340 generates a KEM key 341 using the KEM key mask value 411. A data decrypting part 350 decrypts an encrypted data main body 312 into target data 301 using the KEM key 341.