1. A method of marking a text document &lsqb; 100 &rsqb; through the insertion of inter-word blank characters, said method comprising the steps of: editing &lsqb; 110 &rsqb; the number of said inter-word blank characters of said text document in order to conform to a model thus, obtaining a canonical text document &lsqb; 120 &rsqb;; retaining, from said canonical text document, to further conform to said model, a subset of positions &lsqb; 230 &rsqb; of said inter-word blank characters, said subset of positions in which insertion of blank characters is permitted; computing, using said canonical text document &lsqb; 120 &rsqb; and a secret-key as inputs &lsqb; 130 &rsqb;, a unique combination of positions among said subset of positions; inserting into each position &lsqb; 151 &rsqb; of said unique combination of positions at least one extra blank character thus, obtaining a marked text document &lsqb; 150 &rsqb;.