First information is sent from a contents-information receiver apparatus to a contents-information sender apparatus. The first information includes a combination of certificate information and second information for the contents-information receiver apparatus. The first information further includes a signal of a signature for the combination of the certificate information and the second information. In the contents-information sender apparatus, a determination is made as to whether the combination of the certificate information and the second information in the first information is correct or wrong in response to the signal of the signature in the first information. In the contents-information sender apparatus, the second information is extracted from the first information before being stored. The second information for the contents-information receiver apparatus is sent from the contents-information receiver apparatus to the contents-information sender apparatus. In the contents-information sender apparatus, the sent second information is collated with the stored second information.