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