cryptage et decryptage rsa sur une image utilisant java netbeans - netbeans-8

Question

I'm working on an application that can encrypt and decrypt an image (specific selection ) using RSA algorithm, all works well but some pixels are behaving strangely and I can't understand why! I use the same parameters to encrypt/decrypt and save the image and yet, when I create the new image, and try to read the pixels in crypted zone, I don't get the pixel that my program showed me before.
File img = new File (Path);
bf1 = ImageIO.read(img);
marchdanslImage(bf1,captureRect); // only selected rectangle (captureRect) from image will be treated
///////the function i called before
private void marchdanslImage(BufferedImage image , Rectangle REC) throws IOException {
bf2 = new BufferedImage(REC.width, REC.height, BufferedImage.TYPE_INT_RGB); //this image gonna contain the pixels after encryption
for (int i = y; i < h; i++) {
for (int j = x; j < w; j++) {
int pixel = image.getRGB(j, i);//orginal values
printPixelARGB(pixel,j,i); //here i call the code to crypt or decrypt
bf2.setRGB(j-x,i-y, rgb); //new values
} }
}
the code of the function printPixelARGB:
public void printPixelARGB(int pixel,int i , int j) {
r[i][j] = (pixel >> 16) & 0xff; // original values
rr[i][j] = RSA_crypt_decrypt(r[i][j], appel);//values after treatment
g[i][j] = (pixel >> 8) & 0xff;
gg[i][j] = RSA_crypt_decrypt(g[i][j], appel);
b[i][j] = (pixel) & 0xff;
bb[i][j] = RSA_crypt_decrypt(b[i][j], appel);
rgb = rr[i][j];// new values on rgb to be set in bf2
rgb = (rgb << 8) + gg[i][j];
rgb = (rgb << 8) + bb[i][j];
}
and finally to save my work:
public void save_image()
{
Graphics2D g;
g = (Graphics2D) bf1.getGraphics();
g.drawImage(bf2, captureRect.x, captureRect.y, captureRect.width, captureRect.height, null);
g.dispose();
//i draw the crypted pixels on my original image and create new image
File outputFile = new File("C:/USERS/HP/DesKtop/output.jpg");
try {
ImageIO.write(bf1, "jpg", outputFile);
} catch (IOException ex) {
Logger.getLogger(MenuGenerale2.class.getName()).log(Level.SEVERE, null, ex);
}
}
So far everything is working, but when open the image I created, and try to decrypt, the values I get are not the same, after treatment!
Is it because of the saving part? When I try it on a white image it does not work correctly, but on another image it does not at all! It's been 3 weeks couldn't solve this problem... I really really need help.
Here is the link of my application:
www.fichier-rar.fr/2016/04/23/cryptagersa11/

Answer 1

The problem is that you are saving the image with JPEG compression. JPEG compression does not preserve data exactly: it is a lossy compression.
If you used, say, BMP or PNG files, the problem would would not happen.
You might want to investigate steganography, although I suspect it is the opposite of what you want to achieve