System, apparatus, program and method for obtaining time stamp

A time stamp obtaining apparatus connected with the time stamp providing apparatus, the time stamp providing apparatus transmitting a time stamp generated by updated private key for data, the data including time and received hash value, the time stamp obtaining apparatus comprising:

• a receiving unit configured to receive one of a document data and a hash value calculated from a document data transmitted from a terminal;
• a first calculation section configured to calculate the received hash value of the document data;
• a first transmitting section configured to transmit one of the hash value received from the terminal and the hash value calculated from the document data by the first calculation section to the time stamp providing apparatus;
• a first storing processing section configured to add the time stamp to unupdated data and to store the time stamp in a storage unit when the time stamp generated for the hash value transmitted by the first transmitting section is received from the time stamp providing apparatus, the unupdated data being data concerning the time stamp received from the time stamp providing apparatus since point to which a private key used by the time stamp providing apparatus is updated last time;
• an update detecting section configured to detect update of the private key of the time stamp used by the time stamp providing apparatus;
• a second calculation section configured to calculate one hash value for all time stamps included in the unupdated data when the update detecting section detects the update of the private key;
• a second transmitting section configured to transmit the hash value calculated by the second calculation section to the time stamp providing apparatus;
• and
• a second storing processing section configured to move the unupdated data to past data and store the unupdated data in the storage unit when the time stamp generated for the hash value transmitted by the second transmitting section is received from the time stamp providing apparatus, and to store the newly received time stamp in the storage unit as new unupdated data, the past data being data concerning the time stamp received from the time stamp providing apparatus before point to which private key is updated by the time stamp providing apparatus last time.

A computer-executable program product stored on a non-transitory computer readable medium for obtaining a time stamp, the computer-executable program product when executed by a processor including a method comprising:

• receiving one of a document data and a hash value calculated from a document data transmitted from a terminal;
• calculating the hash value from the received document data;
• transmitting one of the hash value received from the terminal and the hash value calculated from the document data received from the terminal to a time stamp providing apparatus;
• adding the time stamp to the unupdated data which is data concerning the time stamp received from the time stamp providing apparatus since point to which the private key used by the time stamp providing apparatus is updated last time when the time stamp generated with an updated private key is received from the time stamp providing apparatus for data to which time and the transmitted the hash value are included, and storing the time stamp in a storage unit;
• detecting update of the private key of the time stamp used by the time stamp providing apparatus;
• calculating one hash value for all time stamps included in the unupdated data after detecting the update of the private key;
• transmitting the calculated hash value for all time stamps included in the unupdated data to the time stamp providing apparatus;
• and
• moving the unupdated data to past data and storing the unupdated data in the storage unit when the time stamp generated with the updated private key is received from the time stamp providing apparatus for data to which time and the transmitted the hash value are included, and storing the newly received time stamp in the storage unit as new unupdated data, the past data being data concerning the time stamp received from the time stamp providing apparatus before point to which private key is updated by the time stamp providing apparatus last time.

A method of obtaining a time stamp, comprising the step of:

• receiving one of a document data and a hash value calculated from a document data transmitted from a terminal;
• calculating the hash value from the received document data;
• transmitting one of the hash value received from the terminal and the hash value calculated from the document data received from the terminal to a time stamp providing apparatus;
• adding the time stamp to the unupdated data which is data concerning the time stamp received from the time stamp providing apparatus since point to which the private key used by the time stamp providing apparatus is updated last time when the time stamp generated with an updated private key is received from the time stamp providing apparatus for data to which time and the transmitted the hash value are included, and storing the time stamp in a storage unit;
• detecting update of the private key of the time stamp used by the time stamp providing apparatus;
• calculating one hash value for all time stamps included in the unupdated data after detecting the update of the private key;
• transmitting the calculated hash value for all time stamps included in the unupdated data to the time stamp providing apparatus;
• and
• moving the unupdated data to past data and storing the unupdated data in the storage unit when the time stamp generated with the updated private key is received from the time stamp providing apparatus for data to which time and the transmitted the hash value are included, and storing the newly received time stamp in the storage unit as new unupdated data, the past data being data concerning the time stamp received from the time stamp providing apparatus before point to which private key is updated by the time stamp providing apparatus last time.