There is provided an input unit which reads copyright digital data stored in a recording medium such as a CD-ROM, an operation unit which performs encryption of digital data based on an encryption algorithm from a plurality of encryption algorithms. A file unit outputs the digital data encrypted by the operation unit and an index value and the encryption operation equation generation parameter into one file. A reproducing apparatus obtains an encryption operation equation from the index value and the encryption operation equation generation parameter in this same file and reproduces the encrypted digital data.