// (c) 2006 Richard Grimes
// www.grimes.demon.co.uk

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

class App
{
   static void Main(string[] args)
   {
      if (args.Length < 3)
      {
         Console.WriteLine("command line: <input file> <output file> <password> [e|d]");
         Console.WriteLine("\twhere e means encrypt (the default) and d means decrypt");
         return;
      }

      bool bEncrypt = true;
      if (args.Length == 4) bEncrypt = (args[3].ToLower()[0] == 'e');

      FileStream fsIn = new FileStream(args[0], FileMode.Open);
      FileStream fsOut = new FileStream(args[1], FileMode.Create);
      if (bEncrypt) Encrypt(fsIn, fsOut, args[2]);
      else Decrypt(fsIn, fsOut, args[2]);
   }
   static void Encrypt(Stream sIn, Stream sOut, string password)
   {
      Rijndael r = Rijndael.Create();
      byte[] salt = null;
      byte[] pass = null;
      CreatePassword(password, r.KeySize >> 3, r.KeySize >> 3, out pass, ref salt);
      r.Key = pass;
      sOut.Write(salt, 0, salt.Length);
      sOut.Write(r.IV, 0, r.IV.Length);
      CryptoStream cs = new CryptoStream(sIn, r.CreateEncryptor(), CryptoStreamMode.Read);
      byte[] buffer = new byte[1024];
      while (true)
      {
         int read = cs.Read(buffer, 0, buffer.Length);
         if (read == 0) break;
         sOut.Write(buffer, 0, read);
      }
      cs.Close(); // closes sIn
      sOut.Close();
   }
   static void Decrypt(Stream sIn, Stream sOut, string password)
   {
      Rijndael r = Rijndael.Create();
      byte[] salt = new byte[r.KeySize >> 3];
      byte[] pass = null;
      sIn.Read(salt, 0, salt.Length);
      CreatePassword(password, r.KeySize >> 3, r.KeySize >> 3, out pass, ref salt);
      r.Key = pass;
      byte[] IV = new byte[r.IV.Length];
      sIn.Read(IV, 0, IV.Length);
      r.IV = IV;
      CryptoStream cs = new CryptoStream(sOut, r.CreateDecryptor(), CryptoStreamMode.Write);
      byte[] buffer = new byte[1024];
      while (true)
      {
         int read = sIn.Read(buffer, 0, buffer.Length);
         if (read == 0) break;
         cs.Write(buffer, 0, read);
      }
      cs.FlushFinalBlock();
      sIn.Close();
      cs.Close(); // closes sOut
   }
   static void CreatePassword(string phrase, int saltSize, int passSize, out byte[] pass, ref byte[] salt)
   {
      if (salt == null)
      {
         RandomNumberGenerator rand = RandomNumberGenerator.Create();
         salt = new byte[saltSize];
         rand.GetBytes(salt);
      }
      PasswordDeriveBytes pdb = new PasswordDeriveBytes(phrase, salt);
      pass = pdb.GetBytes(passSize);
   }
}