Hiding Your Bits in the Bytes: A basic example of modern steganography using C#

bits_in_bytes.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Linq;
using System.Text;
 
namespace SteganographyTest
{
    class Program
    {
        static void Main()
        {
            byte[] hiddenBytes = Util.BitmapToByteArray(Image.FromFile("hidden.png"));
            Encode(hiddenBytes, "innocuous.png", "encoded.png");
            byte[] loadedHiddenBytes = Decode("encoded.png");
            Util.ByteArrayToBitmap(loadedHiddenBytes).Save("decoded.png", ImageFormat.Png);
            CreateMask("innocuous.png", "encoded.png");
        }
 
        public static void Encode(byte[] hiddenBytes, string inputImageFileName, string outputImageFileName)
        {
            // Loading the data we want to hide to a byte array
            byte[] hiddenLengthBytes = BitConverter.GetBytes(hiddenBytes.Length);
            byte[] hiddenCombinedBytes = Util.Combine(hiddenLengthBytes, hiddenBytes);
 
            // Loading an innocuous image we want to store the hidden data in to a byte array
            Image innocuousBmp = Image.FromFile(inputImageFileName);
            byte[] rgbComponents = Util.RgbComponentsToBytes(innocuousBmp);
 
            // Encoding the hidden data into the innocuous image, and storing it to file.
            byte[] encodedRgbComponents = EncodeBytes(hiddenCombinedBytes, rgbComponents);
            Bitmap encodedBmp = Util.ByteArrayToBitmap(encodedRgbComponents, innocuousBmp.Width, innocuousBmp.Height);
            encodedBmp.Save(outputImageFileName, ImageFormat.Png);
        }
 
        private static byte[] EncodeBytes(byte[] hiddenBytes, byte[] innocuousBytes)
        {
            BitArray hiddenBits = new BitArray(hiddenBytes);
            byte[] encodedBitmapRgbComponents = new byte[innocuousBytes.Length];
            for (int i = 0; i < innocuousBytes.Length; i++)
            {
                if (i < hiddenBits.Length)
                {
                    byte evenByte = (byte)(innocuousBytes[i] - innocuousBytes[i] % 2);
                    encodedBitmapRgbComponents[i] = (byte)(evenByte + (hiddenBits[i] ? 1 : 0));
                }
                else
                {
                    encodedBitmapRgbComponents[i] = innocuousBytes[i];
                }
            }
            return encodedBitmapRgbComponents;
        }
 
        public static byte[] Decode(string imageFileName)
        {
            // Loading the seemingly innocuous image with hidden data into a byte array
            Bitmap loadedEncodedBmp = new Bitmap(imageFileName);
            byte[] loadedEncodedRgbComponents = Util.RgbComponentsToBytes(loadedEncodedBmp);
 
            const int bytesInInt = 4;
            byte[] loadedHiddenLengthBytes = DecodeBytes(loadedEncodedRgbComponents, 0, bytesInInt);
            int loadedHiddenLength = BitConverter.ToInt32(loadedHiddenLengthBytes, 0);
            byte[] loadedHiddenBytes = DecodeBytes(loadedEncodedRgbComponents, bytesInInt, loadedHiddenLength);
            return loadedHiddenBytes;
        }
 
        private static byte[] DecodeBytes(byte[] innocuousLookingData, int byteIndex, int byteCount)
        {
            const int bitsInBytes = 8;
            int bitCount = byteCount * bitsInBytes;
            int bitIndex = byteIndex * bitsInBytes;
            bool[] loadedHiddenBools = new bool[bitCount];
            for (int i = 0; i < bitCount; i++)
            {
                loadedHiddenBools[i] = innocuousLookingData[i + bitIndex] % 2 == 1;
            }
            BitArray loadedHiddenBits = new BitArray(loadedHiddenBools);
            byte[] loadedHiddenBytes = new byte[loadedHiddenBits.Length / bitsInBytes];
            loadedHiddenBits.CopyTo(loadedHiddenBytes, 0);
            return loadedHiddenBytes;
        }
 
        public static void CreateMask(string inputImageFileName1, string inputImageFileName2)
        {
            Image image1 = Image.FromFile(inputImageFileName1);
            Image image2 = Image.FromFile(inputImageFileName2);
            Bitmap bmp1 = new Bitmap(image1);
            Bitmap bmp2 = new Bitmap(image2);
            Bitmap maskDiff = new Bitmap(bmp1);
            Bitmap maskParity1 = new Bitmap(bmp1);
            Bitmap maskParity2 = new Bitmap(bmp2);
 
            for (int i = 0; i < maskDiff.Height; i++)
            {
                for (int j = 0; j < maskDiff.Width; j++)
                {
                    Color px1 = bmp1.GetPixel(j, i);
                    Color px2 = bmp2.GetPixel(j, i);
 
                    int maskDiffIntensity = 255 - Math.Abs(px2.R - px1.R) * 85 - Math.Abs(px2.G - px1.G) * 85 - Math.Abs(px2.B - px1.B) * 85;
                    maskDiff.SetPixel(j, i, Color.FromArgb(maskDiffIntensity, maskDiffIntensity, maskDiffIntensity));
 
                    int maskParityIntensity1 = (px1.R % 2) * 85 + (px1.G % 2) * 85 + (px1.B % 2) * 85;
                    maskParity1.SetPixel(j, i, Color.FromArgb(maskParityIntensity1, maskParityIntensity1, maskParityIntensity1));
 
                    int maskParityIntensity2 = (px2.R % 2) * 85 + (px2.G % 2) * 85 + (px2.B % 2) * 85;
                    maskParity2.SetPixel(j, i, Color.FromArgb(maskParityIntensity2, maskParityIntensity2, maskParityIntensity2));
                }
            }
 
            maskDiff.Save("maskDiff.png");
            maskParity1.Save("maskParity_" + inputImageFileName1);
            maskParity2.Save("maskParity_" + inputImageFileName2);
 
        }
    }
 
    class Util
    {
        public static byte[] BitmapToByteArray(Image img)
        {
            using (MemoryStream ms = new MemoryStream())
            {
                img.Save(ms, ImageFormat.Png);
                return ms.ToArray();
            }
        }
 
        public static Image ByteArrayToBitmap(byte[] bytes)
        {
            using (MemoryStream ms = new MemoryStream(bytes))
            {
                return Image.FromStream(ms);
            }
        }
 
        public static byte[] Combine(byte[] left, byte[] right)
        {
            byte[] combined = new byte[left.Length + right.Length];
            Buffer.BlockCopy(left, 0, combined, 0, left.Length);
            Buffer.BlockCopy(right, 0, combined, left.Length, right.Length);
            return combined;
        }
 
        public static byte[] RgbComponentsToBytes(Image innocuousImg)
        {
            Bitmap innocuousBmp = new Bitmap(innocuousImg);
            int counter = 0;
            byte[] components = new byte[3 * innocuousBmp.Width * innocuousBmp.Height];
            for (int y = 0; y < innocuousBmp.Height; y++)
            {
                for (int x = 0; x < innocuousBmp.Width; x++)
                {
                    Color c = innocuousBmp.GetPixel(x, y);
                    components[counter++] = c.R;
                    components[counter++] = c.G;
                    components[counter++] = c.B;
                }
            }
            return components;
        }
 
        public static Bitmap ByteArrayToBitmap(byte[] rgbComponents, int width, int hight)
        {
            Queue<byte> rgbComponentQueue = new Queue<byte>(rgbComponents);
            Bitmap bitmap = new Bitmap(width, hight);
            for (int y = 0; y < hight; y++)
            {
                for (int x = 0; x < width; x++)
                {
                    bitmap.SetPixel(x, y, Color.FromArgb(rgbComponentQueue.Dequeue(), rgbComponentQueue.Dequeue(), rgbComponentQueue.Dequeue()));
                }
            }
            return bitmap;
        }
    }
}