 The table of primitive polynomials shows how LFSRs can be arranged in Fibonacci or Galois form to give maximal periods.One can obtain any other period by adding to an LFSR that has a longer period some logic that shortens the sequence by skipping some states.LFSRs have long been used as pseudo-random number generators for use in stream ciphers (especially in military cryptography), due to the ease of construction from simple electromechanical or electronic circuits, long periods, and very uniformly distributed output streams.