Patent ID: 7890764

Claim:
A time stamp providing system comprising a time stamp providing apparatus and a time stamp obtaining apparatus, the time stamp providing apparatus connected with the time stamp obtaining apparatus, the time stamp providing apparatus comprising: a time stamp generate section configured to generate a time stamp by using an updated private key for data including time and a hash value received from the time stamp obtaining apparatus; and a time stamp transmission section configured to transmit the time stamp generated by the time stamp generate section to the time stamp obtaining apparatus, and 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 a 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.