Breaking the stream ciphers F-FCSR-H and F-FCSR-16 in real time

In English The F-FCSR stream cipher family has been presented a few years ago. Apart from some flaws in the initial propositions, corrected in a later stage, there are no known weaknesses of the core of these algorithms. Two variants, F-FCSR-H and F-FCSR-16, were proposed in the eSTREAM project, and F-FCSR-H v2 is one of the ciphers selected for the eSTREAM portfolio.
In this paper we present a new and severe cryptanalytic attack on the F-FCSR stream cipher family. We give the details of the attack when applied to F-FCSR-H v2 and F-FCSR-16. The attack requires a few Mbytes of received sequence, and the complexity is low enough to allow the attack to be performed on a single PC within seconds.