An information recording device uses a data storage device such as media having a built-in flash memory. When data is stored in the data storage device, different encryption keys are used for different sectors. Each encryption key is stored in the header of content. By using a single encryption key for a sector consisting of different blocks, the number of stored encryption keys is limited, and the amount of stored key data is reduced. In accordance with the type of encryption processing, for example, the single DES or the triple DES, one or at least two keys are selected for each sector in order to execute encryption or decryption processing on sector data.