US Patent 7975145 Apparatus and program for update of time stamp

A time stamp updating apparatus includes: a time stamp obtaining unit configured to transmit hash value calculated from certification target data to an apparatus for time stamp authority when certification target data is input, to receive time stamp data from the apparatus for time stamp authority, to relate the received time stamp data to certification target data, and stored them in an evidence data storage unit; and a time stamp verification unit configured to calculate logical OR of a validity period of the time stamp data related to certification target data, and to output a period that can go back from time of verification as a period when the certification target data can be certified.