It is an object to provide a method for invalidation and new registration of a storage medium, a method for backup of data stored in a storage medium and for restoration of backup data to a storage medium, and a method for encryption of and application of an electronic signature to data to be backed up, and for decryption of backup data to be restored and verification of a signature. A service device includes a reception unit for receiving a request for data processing regarding a storage medium from a communication terminal device connected to the storage medium, an authentication unit for performing authentication of whether or not the storage medium connected to the communication terminal device is valid, and a database for storing a public key of the storage medium, wherein, when the reception unit receives a request for invalidation of the first storage medium from the communication terminal device, and the authentication unit authenticates the second storage medium connected to the communication terminal device as a valid storage medium, the database deletes the public key of the first storage medium stored in the database.