In principle the inventive method consists in secure sending of a number S=D mod X or of a set of numbers S(j)=D(j) mod X, j=1, . . . ,i, from a sender device 28 to a receiver device 27, whereby X is a product of at least two big prime numbers and D is greater than X, comprising the following steps: picking a random number A or a set of random numbers A(j) by said sender device; calculating in sai