A lower bound on the linear span of an FCSR

We have derived a lower bound on the linear span of a binary sequence generated by a feedback with carry shift register (FCSR) under the following condition: q is a power of a prime such that q=r/sup e/(e/spl ges/2) and r(=2p+1), where both r and p are 2-prime. This allows us to design FCSR stream ciphers similar to previously proposed linear feedback shift register (LFSR) stream ciphers.