S BoXes f(ri 1, ki)= P(s(e(r-o kin There are 8 different s-Boxes 1 for each chunk S-box process maps 6 bit input to 4 bit output S box performs substitution on 4 bits There are 8 possible substitutions in each S box Inner 4 bits are fed into an s box Outer 2 bits determine which substitution is used 1919 S Boxes • f (Ri-1 , Ki ) = P(S(E(Ri-1 )  Ki )) • There are 8 different S-Boxes,1 for each chunk • S-box process maps 6 bit input to 4 bit output • S box performs substitution on 4 bits • There are 8 possible substitutions in each S box • Inner 4 bits are fed into an S box • Outer 2 bits determine which substitution is used