Patent ID: 7412725

Claim:
A copyright protection system, comprising: first encrypting means for encrypting digital information of a work with a first encrypting function, said first encrypting function being specific to the digital information, a digital information processing apparatus including encrypted information receiving means for receiving the digital information encrypted by the first encrypting function, second encrypting means for encrypting the digital information received by the encrypted information receiving means with a second encrypting function, said second encrypting function being specific to a medium recording the digital information, and decrypting information transmitting means for transmitting decrypting information for decrypting the digital information encrypted by the second encrypting function, and a copyright managing server for managing a copyright of the digital information including a receiving device for receiving the decrypting information transmitted from the decrypting information transmitting means, and decrypting function transmitting means for transmitting a decrypting function for decrypting the digital information encrypted by the first encrypting function and the second encrypting function in response to the decrypting information transmitted by the decrypting information transmitting means, wherein said first encrypting function and said second encrypting function use a same function system, said function system having a solution that is a remainder obtained by multiplying the digital information by a matrix to obtain a product and dividing each element of the product by a predetermined prime number.