Patent attributes
In case of a range search to the encryption DB (database), conventionally, because there is a correlation between a value of the data and the number of search keys for the range search, the contents of the encrypted data can be inferred and are not safe. Also, it is not efficient sufficiently in case of insertion of the data, and search. In the present invention, the search keys related by the data are generated for a predetermined number without depending on the value of the data. Also, when the search keys showing a range are generated, the search keys are provided from the search key having a narrow width to the search key having a wide range, and the widths have a relation of a power series length, to suppress the number of necessary search keys.
