| 摘要 |
PROBLEM TO BE SOLVED: To estimate effectiveness of a timestamp even without using all documents when acquiring the timestamp to a group including the plurality of documents. SOLUTION: A registration part 120 combines the document and the timestamp of the group in each document inside the group, calculates a hash value about data of its combination result, and stores it as an attribute of the document. When verification of the timestamp of the document is instructed, a timestamp verification part 170 calculates a hash value of the combination result between the document and the timestamp, and decides whether its calculation result accords with the hash value stored as the attribute of the document or not. The timestamp verification part 170 also performs similar decision about the second document inside the same group when they accord, and decides that the timestamp is effective to the document of a verification target when a determination result of the "accordance" can be also obtained about the second document. COPYRIGHT: (C)2009,JPO&INPIT |
