Information to be recorded is encrypted using an encryption key based on information inherent in a recording medium. The information inherent in the recording medium is specific information on a disk. When an encrypted information recorded on a recording medium is decrypted, there are reproduced from a recording medium a first file storing information encrypted by using an encryption key generated based on a random data to be inserted into a predetermined portion of the encrypted information to be recorded on a recording medium and a second file storing data indicative of a predetermined portion of the random data to be inserted into a predetermined portion of the encrypted information. The random data is detected from the encrypted information. A decryption key is generated from the detected random data. The encrypted information of the reproduced first file is decrypted using the decryption key.