A provider side apparatus provides original digital data together with a
digital signature generated by the provider side apparatus, the digital
signature detecting whether the original digital data was falsified or
detecting a change level given to the original digital data. Upon
reception of the digital data, a receiver side apparatus can know the
originality of the received digital data or a change level of the
received digital data from the original digital data, in accordance with
the digital signature corresponding to the digital data.