1. Method of retrieving encrypted documents stored in a computer memory by performing a boolean search over the encrypted documents, each document being characterized by a set of keywords, the method comprising: forming an index with the set of keywords characterizing the encrypted documents; translating the index in an orthonormal basis in which each keyword of the index corresponds to one and only one vector of the orthonormal basis; associating each document of the set of encrypted documents with a resultant vector in a span of the orthonormal basis, the resultant vector corresponding to each encrypted document stored in an encrypted search server comprising the computer memory; receiving a search query from a querier; transforming the search query into one query matrix; and determining a general result based on the result of the multiplication between the query matrix and each of the resultant vectors to retrieve encrypted documents from the computer that match the search query.