Range search system, range search method, and a range search program

Conventionally, when the range search the encrypted DB (database), since there is a correlation with the number of the search key for the size and range search data values, the contents of the encrypted data is guessable There was no safe. The insertion of the data was not sufficiently efficient in the search. In the present invention, a search key associated with the data, regardless of the size of the data values, a predetermined number, generates. Also, when generating a search key representing a range, served until wider from those width of the range is narrow, and its width by the so that the powers length relationship at the time and data retrieval data insertion reduce the number of search keys required.