A system and a method of querying a remote service without revealing a private document to the remote service are provided. The method includes receiving a signature of a user's private document, and querying an intermediate database with the signature of the private document to generate an intermediate result set comprising intermediate database documents, based on a computation of similarity of the signatures of the intermediate database documents to the signature of the private document. The remote service is queried, based on the intermediate result set and a final result set is received from the remote service based on the query, which can be output to the user or further processed.