The invention relates to a method of inserting a message into digital data representative of physical quantities, the message including ordered symbols, including the steps of: segmenting (E2) the data into regions, associating (E3) at least one region with each symbol to be inserted, characterized in that, for each region into which a symbol in question is to be inserted, it includes the steps of: determining (E7) a pseudo-random function, from a key which depends: on an initial key, and on the length of the message, modulating (E8) the symbol in question by the previously determined pseudo-random function in order to supply a pseudo-random sequence, adding (E10) the pseudo-random sequence to the region in question.