Abstract: 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.

Abstract: It is aimed to prevent access to data when a storage device 1 is lost without damaging security and convenience of a user even if the storage device 1 is under condition in which communication with an authentication server is unavailable and further a personal identification number is leaked. The storage device 1 includes a data storing unit 11 which stores security target data and valid duration of use data showing a valid duration of use of the security target data and a validity checking unit 14 which implements a validity check process for checking if the security target data stored in the data storing unit 10 is valid based on the valid duration of use data stored in the data storing unit 10. Then, when the communication with the authentication server is unavailable, access to the data is controlled by implementing the validity check process.