Based on the investigation of Feedback shift registers with carry operation (FCSR) and F-FCSR-Hv2 key stream generator which was a hardware candidate for eSTREAM

we present a generator named Combined F-FCSR.The random property of Combined F-FCSR is as good as F-FCSR and the key stream sequence passes the test of NIST’s suit STS.By means of simple nonlinear operation

the Combined F-FCSR can resist the Hell-Johansson attack based on the fact that the main register of FCSR automat is linearly shifted at some special situations.