Usage by second content of previously distributed first content, is permitted if the proper electronic signature is incorporated into predetermined data added to the second content. A secret key and a public key are generated for the first content. The public key is added to the first content which is transmitted. When the second content seeks to refer to the first content, an electronic signature, produced by employing the secret key, is requested and incorporated into predetermined data that is added to the second content. The second content with the predetermined data is transmitted. At the receiver, the public key which was added to the first content, is used in a collating process with the received electronic signature, and when the collation succeeds, the previously received first content stored at the receiver is used in accordance with instructions received with the second content.