nK = 17; %for example, length of key
key_sequence = round(rand(1,nK)); %example key
nB = 50; %for example, length of bit sequence
bit_sequence = round(rand(1,nB)); %example bits
new_bits = zeros(1, nB);
for J = 1 : nB
new_bits(J) = xor( bit_sequence(J), key_sequence(mod(J-1, nK)+1) ); %xor with key
end