how discrete wavelet transform used by using a key? To secure the image

if true
  % code
end
X=imread('lena512.bmp');
[LoD,HiD] = wfilters('haar','d');
[cA,cH,cV,cD] = dwt2(X,LoD,HiD,'mode','symh');
colormap gray(255);
subplot(2,2,1);
imagesc(cA);
title('Approximation');
subplot(2,2,2);
imagesc(cH);
title('Horizontal');
subplot(2,2,3);
imagesc(cV);
title('Vertical');
subplot(2,2,4);
imagesc(cD);
title('Diagonal');