Rijndael image encryption problem

Samuel Amantea Collins

Hi i have a problem with Rijndael encryption (I've uploaded the source code). Basically i'm trying to convert an image into byte[] data, run Rijndael encryption on it based on a given password. Then i need to be able to convert that Byte[] data back into a bmp. This is where the problem seems to occur. The line:

tempImage = Image.FromStream(ms, true);

always throws the exception "invalid paramater" meaning that it can't read the byte[] data and convert it into a bmp image. If i take out the Rijndael encryption, there is no problem but for some reason, when i do use it, it seems to give me back an invalid byte[] representation for a bmp?! I've been trying to work out what's going on here for a while and it's getting really frustrating. I'd appreciate any help that can be given.

Also, you may notice that i've used a message box to show me information about the byte data before and after encryption. I did notice that the byte[] data afterwards was 10 larger than before encryption. I don't know why or what this means but it seems to occur first at the line:

byte[] encryptedData = ms2.ToArray();

Thanks in advance :)

3 Replies

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Sam Hobbs15y ago
I am sorry that we were unable to help you. Howsever, yeah, that sure makes sense. I sure don't understand why you were using an image in that manner. If the intent was to hide encrypted data as an image, then first that won't fool the experts but it will work to hide the data from most people. Second it can be done but you just need to research it a bit more. I don't remember the details but essentially you would want to add a header to the bmp file. There are of course many other ways to hide the data such as (I think) a binary resource in a DLL.
Samuel Amantea Collins15y ago
Ok i solved this. Actually, it was an incredibly simple solution. You simply can't read the encrypted data into an image, it's in the wrong format.
Samuel Amantea Collins15y ago
Not sure if the upload worked, so here is the code:

private void SubmitButton_Click(object sender, EventArgs e)
        {

            Bitmap b = (Bitmap)Picture;
            byte[] Bytes = GetBytes(b);
            byte[] EncBytes = Encrypt(Bytes, "sawerfgyujnml");
            /*
            MessageBox.Show("Byte's length = " + Bytes.Length + '\n'
                +"EncByte's length = " + EncBytes.Length + '\n'
                +"Byte's rank = " + Bytes.Rank + '\n'
                +"Enc Byte's rank = " + EncBytes.Rank + '\n'
                +"Byte's Long Lenght = " + Bytes.LongLength + '\n'
                +"EncByte's Long Lenght = " + EncBytes.LongLength + '\n'
                +"Byte's Is fixed size? " + Bytes.IsFixedSize + '\n'
                +"EncByte's Is fixed size? " + EncBytes.IsFixedSize + '\n');
             */
            Image EncPicture = GetImage(EncBytes);
            pictureBox.Image = EncPicture.GetThumbnailImage(pictureBox.Width, pictureBox.Height,
                    ThumbnailCallback, System.IntPtr.Zero);
        }

        private byte[] GetBytes(Bitmap b)
        {
            using (MemoryStream ms = new MemoryStream())
            {
                b.Save(ms, System.Drawing.Imaging.ImageFormat.Bmp);
                byte[] ret = ms.ToArray();
                return ret;
            }
        }

        private Image GetImage(byte[] PictureBytes)
        {
            Image tempImage;
            using (MemoryStream ms = new MemoryStream(PictureBytes, 0, PictureBytes.Length))
            {
                ms.Write(PictureBytes, 0, PictureBytes.Length);
                tempImage = Image.FromStream(ms, true);
                return tempImage;
            }
        }

        public static byte[] Encrypt(byte[] clearData, byte[] Key, byte[] IV)
        {
            MemoryStream ms2 = new MemoryStream();
            Rijndael alg = Rijndael.Create();
            alg.Key = Key;
            alg.IV = IV;
            CryptoStream cs = new CryptoStream(ms2,
               alg.CreateEncryptor(), CryptoStreamMode.Write);
            cs.Write(clearData, 0, clearData.Length);
            cs.Close();
            byte[] encryptedData = ms2.ToArray();
            return encryptedData;
        }

        public static byte[] Encrypt(byte[] clearData, string Password)
        {
            PasswordDeriveBytes pdb = new PasswordDeriveBytes(Password,
                new byte[] {0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d,
            0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76});
            return Encrypt(clearData, pdb.GetBytes(32), pdb.GetBytes(16));
        }

        public bool ThumbnailCallback()
        {
            return false;
        }