The invention relates to a method of watermarking a data set comprising the steps of: selecting, in the data set, at least one group of two data; and modifying at least one data of the group. The data is modified such that the difference between the modified data and the other data of the group possibly modified equals a predefined watermarking parameter multiplied by an integer number, called rejection class, associated with the group and equal to the integer nearest to the ratio between the difference between the at least one data and the other data of the group before the modification divided by the watermarking parameter.