1. Method to perform a boolean search over encrypted documents, each document being characterized by a set of keywords, all the keywords characterizing all the documents forming an index, the index being translated in an orthonormal basis in which each keyword of the index corresponds to one and only one vector of the orthonormal basis, each document being associated with a resultant vector in the span of the orthonormal basis, the resultant vectors corresponding to all the documents being stored in an encrypted search server, the method comprising the steps of: receiving a search query from a querier; transforming the search query in 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.