Abstract: An authentication communication system includes an storage medium having an area for storing digital information and an access device for reading/writing digital information from/into the area. The access device authenticates whether the storage medium is authorized according to a challenge-response authentication protocol in which scrambled access information generated by scrambling the access information which shows the area is used. The storage medium authenticates whether the access device is authorized. When the access device and the storage medium have authenticated each other as authorized devices, the access device reads/writes digital information from/into the area in the storage medium according to the access information separated from the scrambled access information by the access device.

Abstract: A decryption device includes: an internal-key storage section for storing an internal-key; a content-key storage section for storing a content-key; a determination section for determining whether or not a value of the content-key storage section in its initial state and a current value of the content-key storage section are different; and an operation section, the operation section including a first decrypting section which, when an encrypted content-key is input to the operation section, decrypts the encrypted content-key using the internal-key so as to obtain a content-key and stores the content-key in the content-key storage section, and a second decrypting section which, when an encrypted content is input to the operation section and the determination section determines that the value of the content-key storage section in its initial state and the current value of the content-key storage section are different, decrypts the encrypted content using the current value of the content-key storage section as a c