6 insertion and especially uses the initial key k init the following step e 216 is the generation of pseudo random sequences as a function of each of the previously generated keys k the following step e 217 is the calculation of the correlation between the pseudo random sequences generated at the preceding step and the regions selected at step e 213 the following step e 218 calculates the absolute value of the correlation calculated for the current bit and for all the regions which are associated with it if the assumption step e 211 as to the size of the message is false then the value calculated at step e 218 remains low in contrast if the assumption of the size of the message is true then the value calculated at step e 218 is high the following step e 219 is the summing of the absolute value of the correlation calculated for the current symbol with the absolute values of the correlation previously calculated for the other symbols for the message length in question for a given message length the steps e 212 to e 219 are repeated for all the symbols of the message steps e 211 to e 219 are repeated for.