The present invention relates to the field of electric communication and computer engineering, and more particularly, to the field of cryptographic methods and devices for ciphering digital data. The method comprises dividing a block of data N.gtoreq.2 subblocks; converting these subblocks one after another by generating at least one binary vector according to the subblocks value and modifying the subblock using the binary vector. Novelty of the claimed method is in generating the binary vector at the subsequent step of sub-block conversion depending on the binary vector structure at the preceding step of subblock conversion. Novelty is also in generating two binary vectors and converting one of them by operation of cyclic shift on a number of bits equal to the value of the second binary vector. Further, novelty is in modifying one of the subblocks by applying to it a cyclic shifting operation on a number of bits equal to the current value of the binary vector. Novelty is also in the use, in subblock conversion, a number T.gtoreq.2 of stuffing tables, whereby the number (v) of the table is calculated on the basis of the binary vector, and the subblock is modified by a stuffing operation determined by the v-th table.