Database search system, database search method, and non-transitory recording medium

A database search method executed by a computing device including a memory, the method comprising:

• reading a target search instruction including a plurality of criterion, the search instruction being for retrieving information from an encrypted database;
• classifying the plurality of criterion into possible search criteria for the database and impossible search criteria incapable of directly searching the encrypted database;
• generate a plurality of subset search criteria by:
• calculating, regarding the target search instruction, truth values indicating whether or not each of the plurality of subset search criteria, which are subsets of the possible search criteria are satisfied, the plurality of subset search criteria being smaller than the possible search criteria;
• and
• setting the calculated truth values for the plurality of subset search criteria;
• determining whether or not each of the plurality of subset search criteria is inconsistent based on whether criteria of the plurality of subset search criteria is unsatisfied;
• generating third search criteria with using a first subset search criteria, among the plurality of subset search criteria, determined not to be inconsistent, the possible search criteria, and the impossible search criteria;
• obtaining first information extracted from the database in accordance with a search instruction written by using the possible search criteria included in the third search criteria;
• and
• extracting values satisfying the third search criteria among a value included in the first information by executing a search instruction written by using the impossible search criteria included in the third search criteria,
• wherein a second subset search criteria, among the plurality of subset search criteria, that is determined to be inconsistent is not executed as a search instruction.

A non-transitory recording medium that stores a database search program that causes a computer including a memory to implement:

• a target search instruction including a plurality of criterion, the search instruction being for retrieving information from an encrypted database;
• classify the plurality of criterion into possible search criteria for the database and impossible search criteria incapable of directly searching the encrypted database;
• generate a plurality of subset search criteria by:
• calculating, regarding the target search instruction, truth values indicating whether or not each of the plurality of subset search criteria, which are subsets of the possible search criteria, are satisfied, the plurality of subset search criteria being smaller than the possible search criteria;
• and
• setting the calculated truth values for the plurality of subset search criteria;
• determine whether or not each of the plurality of subset search criteria is inconsistent based on whether criteria of the plurality of subset search criteria is unsatisfied;
• generate third search criteria using a first subset search criteria, among the plurality of subset search criteria, determined not to be inconsistent, the possible search criteria, and the impossible search criteria;
• obtain first information extracted from the database in accordance with a search instruct ion written by using the possible search criteria included in the third search criteria;
• and
• extract values satisfying the third search criteria among a value included in the first information by executing a search instruction written by using the impossible search criteria included in the third search criteria,
• wherein a second subset search criteria, among the plurality of subset search criteria, that is determined to be inconsistent is not executed as a search instruction.