f function X32 48 E E(X)48 B l(1-6) B 2(7-12) B B B 5 B B 8(42-48) Cu(1-4) C2 C3 C4 Cs C6 C7 C8(28-32) f×,k)2 16
16 f function x 32 E E(x)48 ki 48 B1(1-6) f(x, ki )32 S1 C1(1-4) B2(7-12) S2 C2 B3 S3 C3 B4 S4 C4 B5 S5 C5 B6 S6 C6 B7 S7 C7 B8(42-48) S8 C8(28-32) + P
f function Combine 32 bit input and 48 bit key into 32 bit output Expand 32 bit input to 48 bits XoR the 48 bit key with the expanded 48 bit input Apply the s-boxes to the 48 bit input to produce 32 bit output Permute the resulting 32 bits 17
17 f function Combine 32 bit input and 48 bit key into 32 bit output • Expand 32 bit input to 48 bits • XOR the 48 bit key with the expanded 48 bit input • Apply the S-boxes to the 48 bit input to produce 32 bit output • Permute the resulting 32 bits
Expansion f(R21,K1)=P(S(E(R21)K)) Expansion E 3212345 456789 8910111213 21314151617 161718192021 202122232425 242526272829 28293031321 18
18 Expansion •f (Ri-1 , Ki ) = P(S(E(Ri-1 ) Ki )) Expansion E : 32 1 2 3 4 5 4 5 6 7 8 9 8 9 10 11 12 13 12 13 14 15 16 17 16 17 18 19 20 21 20 21 22 23 24 25 24 25 26 27 28 29 28 29 30 31 32 1
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 19
19 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
S-Box ·48bits==>32bts.(8*6==>8*4) 2 bits used to select amongst 4 permutations for the rest of the 4-bit quantity 2 bits row I3 O1 O2 4 O3 15 04 4 bits 16 column 8
20 S-Box • 48 bits ==> 32 bits. (8*6 ==> 8 *4) • 2 bits used to select amongst 4 permutations for the rest of the 4-bit quantity 2 bits row Si i = 1,…8. I1 I2 I3 I4 I5 I6 O1 O2 O3 O4 4 bits column