v2 ∗ DECIM

Decim is a hardware oriented stream cipher with 80-bit key and 64-bit IV which was submitted to the ECRYPT stream cipher project. The design of Decim is based on both a nonlinear filter LFSR and an irregular decimation mechanism called the ABSG. As a consequence, Decim is of low hardware complexity. Recently, Hongjun Wu and Bart Preneel pointed out two flaws in the stream cipher Decim. The first flaw concerns the initialization stage and the second one, which is the more serious flaw, concerns the filter used in the keystream generation algorithm; the ABSG mechanism is not affected by these two flaws. In this paper, we propose a new version of Decim, called Decim, which does not only appear to be more secure, but also has a lower hardware complexity than Decim.