US Patent 9785786 Privacy preserving data search

Database entries can be protected by indexing the entries using a plurality of indexes, each associated with a level of access rights. A level of access rights can be determined from a search query, and an index can be selected based on the determined level of access rights. A search key can be generated based on the received query, and the selected index can be searched using the search query. Database entries mapped to the values of the selected index returned in response to the search can be outputted. Each index is associated with a different granularity defining the number and/or ambiguity of search results returned in response to searching an index.