I am new to matlab programming and trying to work with RC4 code [source:http://www.cryptosmith.com/archives/621]. I am trying to get a message encrypted with a key but after getting key stream I am stuck while doing xor of the data. I probably am making mistakes in several places as my result is showing 0 all through. The make function code I am having problem is:
function w = rc4make(n,k)
% rc4make - makes a vector of "n" RC4 outputs of key "k"
sc = rc4key(k);
l = [];
j0 = 0;
i0 = 0;
for s0 = 1:n
[r, i0, j0, sc]=rc4out(i0, j0, sc);
l =[l r];
L1 = logical(n);
disp(L1);
L2 = logical(l);% converting into logical array
disp(L2);
w = xor(L1,L2);
end
function sc=rc4key(key)
% rc4key - return key schedule array for key k
% SEEMS BROKEN - bytes 2-9 are swapped with other key schedule bytes
% At best, not compatible with 'real' RC4. At worst, also more vulnerable
% set up the array
le = length(key);
sc = 0:255;
j0 = 0;
% scramble the key schedule
for i0 = 0:255
k0 = floor(key( floor(mod(i0,le))+1 ));%floor rounds the number into round figure
j0 = floor(mod( j0 + k0 + sc(i0+1), 256));
tm = sc(i0+1);
sc(i0+1) = sc(j0+1);
sc(j0+1) = tm;
end
function [r, i0, j0, sc]=rc4out(i0, j0, sc)
% next byte of rc4 output
% inputs: i0, j0 = indices; sc = key schedule
% outputs: r=random byte; i0, j0 = indices; sc = key schedule
%for q=0:strlen(data)
i0 = mod( (i0+1), 256);
j0 = mod( j0 + sc(i0+1), 256);
tmp = sc(j0+1);
sc(j0+1) = sc(i0+1);
sc(i0+1) = tmp;
r = mod(sc(i0+1) + sc(j0+1), 256);%(S[i]+S[j]) %256
The function I am calling is: rc4make(12,'hi')
where 12 is the plaintext and hi is the key. Could you please guide me to understand my code's problem and please suggest to get the ciphertext properly.