An Improved Attack on WG Stream Cipher

WG is a synchronous stream cipher submitted to the hardware profile of eSTREAM project. The main feature of this stream cipher is the use of WG transformation. WG uses keys and initial vectors (IVs) of the same lengths 80, 96, 112 and 128 bits. Moreover, IVs of the length 32 and 64 bits are admitted. The most important key recovery attack on WG was presented by Wu and Preneel and uses the weakness of the initialization step of the algorithm. The attack is a chosen IV one which its success probability for WG with 80 bit (or more) and 64 bit IVs is close to 1 and , respectively. The attack cannot be performed on WG with IVs of the length 32 bits. In this paper Wu and Preneel’s attack is improved in such a way that the success probability increases nearly to 1 for IVs of length 64 and 32 bits. 5 2