Data decryption device, attribute-based encryption system, random number element removal device, data decryption method, and data decryption program

摘要

An object of the present invention is to improve the security of encrypted data by executing the decryption process of the attribute-based encryption method in a plurality of stages. The KEM key partial decryption unit 320 uses an r-user secret key 221 including a random number element in a user secret key generated by an attribute-based encryption method, and a common key encrypted using an attribute conditional expression. By decrypting a certain encrypted KEM key 313, an r-KEM key mask value 321 including a random number element is generated. The random number element removal request unit 330 requests the IC card 400 to remove the random number element from the r-KEM key mask value 321, and acquires the KEM key mask value 411 from the IC card 400. The mask removal unit 340 generates the KEM key 341 using the KEM key mask value 411. The data decryption unit 350 decrypts the target data 301 from the encrypted data body 312 using the KEM key 341.