In a user terminal, a public key, a master key and a public parameter are generated. An ID including an identifier, an issue date and a validity period of a secret key for service is generated. The secret key is generated based on the master key and the ID. The ID and the secret key are transmitted to a service providing server. The public key and the public parameter are transmitted to a data storage device. In the service providing server, signature data is generated based on the ID and the secret key. A data request, the signature data and the ID are transmitted to the data storage device. In the data storage device, the data request is verified based on the signature data, the public key and the public parameter. When the data request is verified, measurement data of a target device is transmitted to the service providing server.