RM1[a]=Z[a]^RM1[PboxRM[a]];
RM1[a+1]=Z[a+1]^RM1[PboxRM[a+1]];
RM1[a+2]=Z[a+2]^RM1[PboxRM[a+2]];
RM1[a+3]=Z[a+3]^RM1[PboxRM[a+3]];
RM1[a]=Z[a]^RM1[PboxRM[a]];
RM1[a+1]=Z[a+1]^RM1[PboxRM[a+1]];
RM1[a+2]=Z[a+2]^RM1[PboxRM[a+2]];
RM1[a+3]=Z[a+3]^RM1[PboxRM[a+3]];