US Patent 9311494 Secure search method and secure search device

In search that uses searchable code, the search query and the secure index is collated in round-robins fashion, registering the required secure index and a characteristic quantity of deposited data in a database server to realize the searchable code. The server uses the characteristic quantity to perform clustering on the secure index. For search, collation is first performed only for representative data of a cluster. For a hit, the collation priority is raised for all the data included in the cluster. When there is no hit, the priority is lowered. After calculating the priority, collation is performed sequentially for all the data on the basis of the priority.