% Routine 4.3  encryption 
B = rand(m,n);          % choose a blurring matrix
save blur B
                 % blur the image via circular convolution:
Xhat = fft2(X);
Bhat = fft2(B);
Yhat = Bhat.*Xhat;
Y = ifft2(Yhat);
Y = real(Y);
Y = round(Y);
%
% to see how scambled the data, rescale:
Z= Y/(m*n);
a = min(min(Z));
Z = Z - a;
b = max(max(Z));
Z = Z*64/b;
image(Z)               % display the encrypted image
colormap gray
axis off