Program.cs

Program.cs

using System;
using System.Collections.Generic;
using System.IO;

namespace SomethingWrong
{
    class Program
    {
        static char[] key = new char[] {
            (char)0x46, (char)0x75, (char)0x63, (char)0x6B, (char)0x4D, (char)0x69,
            (char)0x63, (char)0x72, (char)0x6F, (char)0x73, (char)0x6F, (char)0x66,
            (char)0x74, (char)0x31, (char)0x32, (char)0x33
        };

        static List<char> output = new List<char>();

        static void Main(string[] args)
        {
            int i = 0;

            using (StreamReader sr = new StreamReader("encrypt_data"))
            {
                while (sr.Peek() >= 0)
                {
                    char c = (char)sr.Read();
                    output.Add((char)(key[i % 16] ^ c ^ (char)(i % 255)));
                    i++;
                }
            }

            Console.WriteLine(new string(output.ToArray()));
        }
    }
}