Authentication apparatus according to the challenge-response principle

In the first devices, MPU 53 generates random number R1 as challenge data. Random number R3 is generated by first encryption IC 54, and then combined with random number R1, encrypted, and sent to second device 52 as encrypted text C1. When encrypted text C2 is similarly received from second device 52, first encryption IC 54 decrypts C2 and separates the decrypted result into first separated data RR2 and second separated data RR4. The first encryption IC 54 returns the first separated data to second device 52 as response data. MPU 53 compares the first separated data returned from second device 52 with random number R1, and in the event of a match, authenticates second device 52 as a legitimate device. The first encryption IC 54 generates the time-varying data transfer key by combining second separated data RR4 with random number R3, and transfers the digital copyrighted data to second device 52 by using the data transfer key.