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

摘要

A device and method enhancing security of encrypted data by dividing a decrypting process of an attribute-based encryption scheme into plural stages. A KEM key partly decrypting part generates an r-KEM key mask value including a random number element, by performing a decrypting process for an encrypted KEM key being a common key encrypted using an attribute conditional expression, using an r-user secret key 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 requests an IC card to remove the random number element from the r-KEM key mask value, and acquires a KEM key mask value from the IC card. A mask removing part generates a KEM key using the KEM key mask value. A data decrypting part decrypts an encrypted data main body into target data using the KEM key.