Stream codes on the basis of shift registers were actively used in the years of war, even long before emergence of electronics. They were simple in design and realization. In 1965 Ernst Selmer, the main cryptographer of the Norwegian government, developed the theory of sequence of shift registers. Later Solomon Golomb, the mathematician of the U.S. National Security Agency, wrote the book under the name "Shift Register Sequences" ("Sequences of shift registers") in which stated the main achievements in this area, and also Selmer's achievements.