containers challenge's builder code.

conrainers.cs

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;

namespace build
{
    class Program
    {
        static void Main(string[] args)
        {
            var flag = "ctf4b{e52df60c058746a66e4ac4f34db6fc81}";
            var font = new Font("Consolas", 100);

            var python = "import hashlib\r\nprint('Valid flag.' if hashlib.sha1(input('Please your flag:').encode('utf-8')).hexdigest()=='"+BitConverter.ToString(SHA1.Create().ComputeHash(Encoding.UTF8.GetBytes(flag))).Replace("-","").ToLower()+"' else 'wrong.'";

            File.WriteAllBytes("..\\..\\..\\..\\..\\files\\challenge", 
                Enumerable.Concat(
                    Enumerable.Concat(
                Enumerable.Concat(Encoding.UTF8.GetBytes("CONTAINER."),
                    flag.Select(e =>
                    {
                        var img = new Bitmap(128, 128);
                        using (var graphics = Graphics.FromImage(img))
                        {
                            graphics.FillRectangle(Brushes.White, 0, 0, img.Width, img.Height);
                            graphics.DrawString(e.ToString(), font, Brushes.SeaGreen, 0, -20);
                        }

                        return img;
                    }).Select((e, i) =>
                    {
                        var stream = new MemoryStream();
                        e.Save(stream, ImageFormat.Png);

                        return stream.ToArray();
                    }).SelectMany((e, i) => Enumerable.Concat(Encoding.UTF8.GetBytes("FILE" + i + "."), e))
                ),
                Encoding.UTF8.GetBytes("VALIDATOR."+python)),
                Encoding.UTF8.GetBytes(".ENDCONTAINER")).ToArray()
            );
        }
    }
}