We propose a novel FCSR-based cryptographic primitive for efficiently resisting M.Hell and T.Johansson's real-time crypt-analysis on FCSR-based stream ciphers.With this proposed primitive in the application

we simply need to xor the bit in the carry unit with the corresponding state bit in a LFSR.Then just perform the original operation of the FCSR.Analysis and experimental results show that:the transition function of the proposed primitive is still quadratic

thus it provides an intrinsic resistance to algebraic attacks and correlation attacks;and it is very important that all the sequences generated by the carry cells are independent

unbiased and have good statistical properties

thus can prevent the attack of Hell and Johansson and other similar attacks on FCSR-based stream ciphers.