The SFLASH cryptographic scheme is a C^＊-scheme with specific parameters.It has been broken by Dubois et al with differential cryptanalytic attacks.This paper reviews the basic attacks to the SFLASH scheme,and points out that a successful attack mainly depends on the symmetry of the SFLASH scheme.Moreover,the symmetry of the C^＊-scheme is investigated,and the fact that projection can break the symmetry of the C^＊-scheme is also strictly proved.The results indicate that the SFLASH scheme with projection can effectively withstand diffe-rential attacks.