A simple app to decode #PurpleFoxEK stegano payloads

Program.cs

using System;
using System.Drawing;
using System.IO;

namespace PurpleFoxPNGDec
{
	internal class Program
	{
		public static int getPrintableLen(byte[] array)
		{
			int i = 0;
			for (i = 0; i < array.Length; i++)
			{
				byte c = array[i];
				var isPrintable = (c >= 0x20 && c < 0x7f) || Char.IsWhiteSpace((char)c);
				if (!isPrintable)
				{
					break;
				}
			}
			return i;
		}

		public static byte[] decode(Bitmap bm, int maxX, int maxY)
		{
			byte[] outData = new byte[maxX * maxY];
			for (int i = 0; i < outData.Length; i++)
			{
				outData[i] = 0;
			}
			for (int y = 0; y < maxY; y++)
			{
				for (int x = 0; x < maxX; x++)
				{
					Color pixel = bm.GetPixel(x, y);
					outData[y * maxX + x] = (byte)(pixel.B * 16 | pixel.G & 0xF);
				}
			}
			return outData;
		}

		private static int Main(string[] args)
		{
			if (args.Length < 2)
			{
				Console.WriteLine("Decoder for Purple Fox stegano components");
				Console.WriteLine("Arguments: <input: PNG> <ouput: decoded>");
				Console.ReadKey();
				return 0;

			}
			string inPath = Path.GetFullPath(args[0]);
			string outPath = Path.GetFullPath(args[1]);
			Console.WriteLine(inPath);

			Bitmap bitmap = new Bitmap(inPath);
			int maxX = bitmap.Width;
			int maxY = bitmap.Height;

			byte[] array = Program.decode(bitmap, maxX, maxY);
			int len = getPrintableLen(array);

			Console.WriteLine("Decoded size: " + len);
			Array.Resize(ref array, len);
			try {
				File.WriteAllBytes(outPath, array);
			} catch (Exception e)
			{
				Console.Write("[ERROR]" + e.Message);
				return (-1);
			}
			Console.Write("Saved output to: " + outPath);
			return 0;
		}
	}
}

Sample of the stegano payload:

• https://www.virustotal.com/gui/file/09998105a542b32ef4f6178af9d4702837d1275aa0fda25b24242d8351980cfa/detection