Content data reproduction system and recording device

A recording device external to a host device, provided in cooperation with the host device, and configured to be capable of decrypting an encrypted content data to allow content data to be used in the host device, the encrypted content data being content data encrypted by content key data, the recording device comprising:

• a first storage area that stores, in a hidden area inaccessible by the host device, a service key;
• a second storage area that stores an encrypted content key data which is the content key data encrypted by the service key, input data to be fed to a host function possessed by an authorized host device, and an encrypted output data which is first output data encrypted by the service key;
• and
• a processor configured to:
• provide the input data to the host device;
• convert the first output data to first converted data by inputting the first output data and session key data into a one-way function;
• receive second converted data obtained by the host device based on the input data, the host function, and the session key data;
• decrypt the encrypted content key data by using the service key to obtain the content key data;
• and
• compare the second converted data with the first converted data, wherein when based on the comparison, the processor determines that the first converted data and the second converted data match each other, the processor is further configured to:
• encrypt the decrypted content key data using the session key;
• and
• send the content key data encrypted by the session key to the host device.