/*
 * Util.Decrypt.cs
 * Authors: Mike Dapiran, Adam Nabinger
 *	based on code by August Zinsser
 * Copyright (c) 2007-2008 Cornell University

 This program is free software; you can redistribute it and/or
 modify it under the terms of the GNU General Public License
 as published by the Free Software Foundation; either version 2
 of the License, or (at your option) any later version.

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.

 You should have received a copy of the GNU General Public License
 along with this program; if not, write to the Free Software
 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
*/

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

namespace Util
{
	/// <summary>
	/// This function is based on the Microsoft tutorial http://support.microsoft.com/kb/307010
	/// </summary>
	public static class Decrypt
	{
		#region Constants

		// Key string constant to encode with
		private const string key = "theautis";

		#endregion

		#region Fields

		// Allows access to the Data Encryption Standard algorithm
		private static readonly DESCryptoServiceProvider DES;

		#endregion

		#region Creation

		/// <summary>
		/// Constructor
		/// </summary>
		static Decrypt()
		{
			//A 64 bit key and IV is required for this provider.
			DES = new DESCryptoServiceProvider();
			//Set secret key For DES algorithm.
			DES.Key = Encoding.ASCII.GetBytes(key);
			//Set initialization vector.
			DES.IV = Encoding.ASCII.GetBytes(key);
		}

		#endregion

		#region Decryption/Encryption

		/// <summary>
		/// Decrypts the given config file assuming that tAC_Encrypt.exe encrypted it. This is done solely to 
		/// hide the config file from the user.
		/// </summary>
		/// <param name="inputFileName">Encrypted File</param>
		/// <returns>The ascii-formatted decrypted contents of the input file</returns>
		[DebuggerHidden]
		public static string DecryptFile(string inputFileName)
		{
			//Create a file stream to read the encrypted file back.
			using (FileStream fsread = new FileStream(inputFileName, FileMode.Open, FileAccess.Read, FileShare.Read))
			//Create a DES decryptor from the DES instance.
			using (ICryptoTransform desdecrypt = DES.CreateDecryptor())
			//Create crypto stream set to read and do a DES decryption transform on incoming bytes.
			using (CryptoStream cryptostreamDecr = new CryptoStream(fsread, desdecrypt, CryptoStreamMode.Read))
			using (StreamReader sr = new StreamReader(cryptostreamDecr))
			{
				return sr.ReadToEnd();
			}
		}

		/// <summary>
		/// Encrypts the given file and saves it into a new file
		/// </summary>
		/// <param name="sInputFilename">The name of the unencrypted file being loaded</param>
		/// <param name="sOutputFilename">The name of the encrypted file being saved</param>
		[DebuggerHidden]
		public static void EncryptFile(string sInputFilename, string sOutputFilename)
		{
			using (FileStream stream = new FileStream(sInputFilename, FileMode.Open, FileAccess.Read))
			using (FileStream stream2 = new FileStream(sOutputFilename, FileMode.Create, FileAccess.Write))
			using (ICryptoTransform transform = DES.CreateEncryptor())
			using (CryptoStream stream3 = new CryptoStream(stream2, transform, CryptoStreamMode.Write))
			{
				byte[] buffer = new byte[stream.Length];
				stream.Read(buffer, 0, buffer.Length);
				stream3.Write(buffer, 0, buffer.Length);
			}
		}

		#endregion
	}
}