The present invention provides a data processing method for encrypting or decrypting contents data using contents key data. The method comprises generating the reference information including data encrypted from contents key data using a plurality of device key data proper to a plurality of apparatus, by encrypting the contents key data using the device key data associated with those of the plural apparatus for which recording or reproduction is allowed, supplying the generated reference information along with the device key data to the plural apparatus, decrypting the contents key data from the supplied reference information, by the plural apparatus, using the device key data proper to the plural apparatus, and encrypting or decrypting the contents data using the decrypted contents key data.