To ensure and facilitate the proof/guarantee of authentication of data in a system, which converts data of a binary form into an XML form to be relayed and which uses the data.

In a method in which a data generation device 1 adds a digital signature to data of a binary form to be transmitted to a relay device 2, the data relay device converts the binary form data into an XML form data to be transmitted to a data usage device 3, and the data usage device proves/guarantees an authentication of data by the digital signature, the data generation device temporarily generates the XML form data corresponding to the binary form data, and prepares the digital signature corresponding thereto to be transmitted to the data relay device. In the preparation of the digital signature, the XML form data is generated from the binary form data per processing block of a message digest, and the message digest corresponding to the XML form data per block is prepared. WS-Security specification is also supported.