Windows7でフォルダ内のテキストファイルをAES暗号化するプログラム

下記のコードをmyenc.cs というファイル名で保存

using System;
using System.IO;
using System.Text;
using System.Security.Cryptography;

public class MyEncrypt {

  static void DoIt(string dir) {
    Directory.CreateDirectory(@"result");
    string[] files = Directory.GetFiles(dir);
    foreach (string fromFile in files) {
      FileStream infs  = new FileStream(fromFile, FileMode.Open);
      StreamReader reader = new StreamReader(infs);
      string input = reader.ReadToEnd();
      reader.Close();
      infs.Close();

      FileStream outfs = new FileStream(fromFile + ".enc", FileMode.Create);
      StreamWriter writer = new StreamWriter(outfs);
      writer.WriteLine(Encrypt(input));
      writer.Close();
      outfs.Close();

      FileStream fstream  = new FileStream(fromFile + ".enc", FileMode.Open);
      StreamReader freader = new StreamReader(fstream);
      string result = freader.ReadToEnd();
      Console.WriteLine(Decrypt(result));
      freader.Close();
      fstream.Close();
    }
  }

  static void Main(string[] args) {
    DoIt(@".\source");
  }

  private const string AesIV = @"PBAErCkB4N5tnJ4=";
  private const string AesKey = @"oSgbUTlzlR5Rsza=";

  static string Encrypt(string text)
  {
      AesCryptoServiceProvider aes = new AesCryptoServiceProvider();
      aes.BlockSize = 128;
      aes.KeySize = 128;
      aes.IV = Encoding.UTF8.GetBytes(AesIV);
      aes.Key = Encoding.UTF8.GetBytes(AesKey);
      aes.Mode = CipherMode.CBC;
      aes.Padding = PaddingMode.PKCS7;

      byte[] src = Encoding.Unicode.GetBytes(text);

      using (ICryptoTransform encrypt = aes.CreateEncryptor())
      {
          byte[] dest = encrypt.TransformFinalBlock(src, 0, src.Length);
          return Convert.ToBase64String(dest);
      }
  }

  static string Decrypt(string text)
  {
      AesCryptoServiceProvider aes = new AesCryptoServiceProvider();
      aes.BlockSize = 128;
      aes.KeySize = 128;
      aes.IV = Encoding.UTF8.GetBytes(AesIV);
      aes.Key = Encoding.UTF8.GetBytes(AesKey);
      aes.Mode = CipherMode.CBC;
      aes.Padding = PaddingMode.PKCS7;

      byte[] src = System.Convert.FromBase64String(text);
      using (ICryptoTransform decrypt = aes.CreateDecryptor())
      {
          byte[] dest = decrypt.TransformFinalBlock(src, 0, src.Length);
          return Encoding.Unicode.GetString(dest);
      }
  }  
}

Windows7にインストールされているCSCでコンパイル

set PATH=C:\Windows\Microsoft.NET\Framework\v3.5;%PATH%
csc myenc.cs