fk.m

SDES encryption algorithm

function [out]= Fk(in,K)
S0=[1 0 3 2;3 2 1 0;0 2 1 3;3 1 3 2];
S1=[0 1 2 3;2 0 1 3;3 0 1 3;2 1 0 3];
left=[in(1:4)];
right=[in(5:8)];
%Expansion function
E=[in(8) in(5) in(6) in(7) in(6) in(7) in(8) in(5)];
S=bitxor(E,K);
y0=de2bi(S0(bi2de([S(1) S(4)])+1,bi2de([S(2) S(3)])+1),2);
y1=de2bi(S1(bi2de([S(5) S(8)])+1,bi2de([S(6) S(7)])+1),2);
h=[y0 y1];
%permutation P4
P4=intrlv(h,[2 4 3 1]);
d=bitxor(left,P4);
g=[d right];
out=g;
%end of function