// Author: SkyOut
// Website: http://wired-security.net
// Date: September 2008
// Version: 1.0 Beta
// Contact: skyout[-at-]wired-security[-dot-]net
//
// For additional help check README.txt

using System;
using System.IO;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            // The EXE gets called like this:
            // patch.exe original_program.exe patched_program.exe offset_to_jump_to byte_to_write
            // Example call:
            // patch.exe crackme.exe crackme_cracked.exe 0000067B EB
            // -> This will write EB at offset 0000067B and generate the new file crackme_cracked.exe
            // (without touching the original file!)

            // Make sure the program gets four arguments as input
            if (args.Length == 4)
            {
                string FileInput = args[0]; // What file to patch?
                string FileOutput = args[1]; // What file to generate?
                string offset = args[2]; // At what offset shall the byte be changed?
                string bytes = args[3]; // What shall be written as the new bytes value?

                // Open all necessary streams and build a BinaryReader/Writer class
                Stream FileToBePatched = File.Open(FileInput, FileMode.Open);
                Stream FileToBeWritten = File.Create(FileOutput);
                BinaryReader BinRead = new BinaryReader(FileToBePatched);
                BinaryWriter BinWrite = new BinaryWriter(FileToBeWritten);

                // Parse the offset
                int i = int.Parse(offset, System.Globalization.NumberStyles.HexNumber);
                // Parse the (new) byte
                byte b = byte.Parse(bytes, System.Globalization.NumberStyles.HexNumber);
                // Write the new file till the offset
                BinWrite.Write(BinRead.ReadBytes(i));
                // Write the new byte into the file
                BinWrite.Write(b);
                // Skip one byte (the one we just changed)
                BinRead.ReadBytes(1);
                // Read the rest of the file and write it
                byte[] r = BinRead.ReadBytes((int)(FileToBePatched.Length - 1));
                BinWrite.Write(r);

                // Close everything!
                FileToBePatched.Close();
                FileToBeWritten.Close();
                BinRead.Close();
                BinWrite.Close();
            }
        }
    }
}