9. The method of claim 1 , wherein the computation of the relevance factors is based on coefficients that minimize the reconstruction error between the signatures of the documents of the intermediate result set and the signature of the private document.
1. A method of querying a remote service without revealing a private document to the remote service, comprising: at a main computer, receiving from a client a signature generated from a user's private document, without receiving the document; 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; computing a relevance factor for each document of the intermediate result set; computing a reconstruction error based on the relevance factors of all the documents in the intermediate result set and determining a confidence in the intermediate result set based on the reconstruction error; querying the remote service with a query which is based on the intermediate result set, whereby the user's private document and the signature of the private document are not revealed to the remote service; receiving a final result set from the remote service based on the query; and weighting the final result set based on the relevance factors.