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

namespace CSEncryptDecrypt
{
   class Class1
   {
      //  Call this function to remove the key from memory after use for security
      [System.Runtime.InteropServices.DllImport("KERNEL32.DLL", EntryPoint="RtlZeroMemory")]
      public static extern bool ZeroMemory(IntPtr Destination, int Length);
		
      // Function to Generate a 128 bits Key.
      static string GenerateKey() 
      {
         // Create an instance of Symetric Algorithm. Key and IV is generated automatically.
         RijndaelManaged aesCrypto = new RijndaelManaged();
         aesCrypto.KeySize = 128;
         // Use the Automatically generated key for Encryption. 
         return ASCIIEncoding.ASCII.GetString(aesCrypto.Key);
      }

      static void EncryptFile(string sInputFilename,
         string sOutputFilename, 
         string sKey) 
      {
         
         FileStream fsInput = new FileStream(sInputFilename, 
            FileMode.Open, 
            FileAccess.Read);

         FileStream fsEncrypted = new FileStream(sOutputFilename, 
            FileMode.Create, 
            FileAccess.Write);
         RijndaelManaged AES = new RijndaelManaged();
         int blockSize = AES.BlockSize/8; // in bytes
         byte[] bytearrayinput = new byte[blockSize];
         long numBlocks = fsInput.Length / blockSize;
         AES.Key = ASCIIEncoding.ASCII.GetBytes(sKey);
         AES.IV = ASCIIEncoding.ASCII.GetBytes(sKey);
         AES.Mode = CipherMode.CBC;
         ICryptoTransform aesencrypt = AES.CreateEncryptor();
         CryptoStream cryptostream = new CryptoStream(fsEncrypted, 
            aesencrypt, 
            CryptoStreamMode.Write); 
         for(long l = 0; l < numBlocks; l++)
         { 
             fsInput.Read(bytearrayinput, 0, bytearrayinput.Length);
             cryptostream.Write(bytearrayinput, 0, bytearrayinput.Length);
         }
         // process last incomplete block if there is one
         if (fsInput.Length % blockSize > 0L)
         {
             bytearrayinput = new byte[fsInput.Length % blockSize];
             fsInput.Read(bytearrayinput, 0, bytearrayinput.Length);
             cryptostream.Write(bytearrayinput, 0, bytearrayinput.Length);
         } 
         
         cryptostream.Close();
         fsInput.Close();
         fsEncrypted.Close();
      }

      static void DecryptFile(string sInputFilename, 
         string sOutputFilename,
         string sKey)
      {

         //Create a file stream to read the encrypted file back.
         FileStream fsInput = new FileStream(sInputFilename, 
            FileMode.Open, 
            FileAccess.Read);

         //Create a file stream to write the decrypted file to disk
         FileStream fsDecrypted = new FileStream(sOutputFilename, 
            FileMode.Create, 
            FileAccess.Write);
         
         RijndaelManaged AES = new RijndaelManaged();         
         //A 128 bit key and IV is required for this provider.
         
         int blockSize = AES.BlockSize/8; // in bytes
         byte[] bytearrayinput = new byte[blockSize];
         long numBlocks = fsInput.Length / blockSize;
         //Set secret key For DES algorithm.
         AES.Key = ASCIIEncoding.ASCII.GetBytes(sKey);
         //Set initialization vector.
         AES.IV = ASCIIEncoding.ASCII.GetBytes(sKey);         
         AES.Mode = CipherMode.CBC;
                         
         //Create a DES decryptor from the DES instance.
         ICryptoTransform aesdecrypt = AES.CreateDecryptor();
         //Create crypto stream set to read and do a 
         //AES decryption transform on incoming bytes.
         CryptoStream cryptostreamDecr = new CryptoStream(fsInput, 
            aesdecrypt,
            CryptoStreamMode.Read);
         for(long l = 0; l < numBlocks - 1; l++)
         { 
             cryptostreamDecr.Read(bytearrayinput, 0, bytearrayinput.Length);
             fsDecrypted.Write(bytearrayinput, 0, bytearrayinput.Length);
         }

         // process last block
         bytearrayinput = new byte[blockSize]; // make sure all bytes are initially zero
         cryptostreamDecr.Read(bytearrayinput, 0, bytearrayinput.Length);
         int len = blockSize;
         for (int i = blockSize - 1; i >= 1; i--)
         {
            if (bytearrayinput[i] != 0) break;
            len = i;
         }
    
         fsDecrypted.Write(bytearrayinput, 0, len);             

         cryptostreamDecr.Close();
         fsInput.Close();
         fsDecrypted.Close();
      } 

      static void Main()
      {
         // Must be 128 bits, 16 bytes.
         // Distribute this key to the user who will decrypt this file.
         string sSecretKey;
         
         // Get the Key for the file to Encrypt.
         sSecretKey = GenerateKey();
         
         // For additional security Pin the key.
         GCHandle gch = GCHandle.Alloc( sSecretKey,GCHandleType.Pinned );
         
         // Encrypt the file.     
         EncryptFile(@"C:\MyData.txt", 
            @"C:\Encrypted.txt", 
            sSecretKey);          
 
         // Decrypt the file.
         DecryptFile(@"C:\Encrypted.txt", 
            @"C:\Decrypted.txt", 
            sSecretKey);

         // Remove the Key from memory. 
         ZeroMemory(gch.AddrOfPinnedObject(), sSecretKey.Length * 2);
         gch.Free();
      }
   }
}

private void decryptFile(byte[] key, byte[] iv, int keySize, CipherMode CM, FileStream fileInput, FileStream fileOutput)
{
    try
    {
        RijndaelManaged AES = new RijndaelManaged();

        AES.IV = iv;
        AES.Mode = CM;
        AES.Key = key;
        AES.KeySize = keySize;

        int blockSize = 16;
        byte[] byteArrayInput = new byte[blockSize];
        long numBlocks = fileInput.Length / blockSize;
        long numBlocksDone = 0;

        ICryptoTransform aesDecrypt = AES.CreateDecryptor();
        CryptoStream cryptoStream = new CryptoStream(fileInput, aesDecrypt, CryptoStreamMode.Read);

        for (long l = 0; l < numBlocks - 1; l++) // now numBlocks - 1
        {
           cryptoStream.Read(byteArrayInput, 0, byteArrayInput.Length);
           fileOutput.Write(byteArrayInput, 0, byteArrayInput.Length);

           numBlocksDone++;
           reportWhileEncrypting(numBlocksDone, numBlocks);
        }

        // process last block
        byteArrayInput = new byte[blockSize]; // make sure all bytes are initially zero
        cryptoStream.Read(byteArrayInput, 0, byteArrayInput.Length);
        int len = blockSize;
        for (int i = blockSize - 1; i >= 1; i--)
        {
           if (byteArrayInput[i] != 0) break;
           len = i;
        }
    
        fileOutput.Write(bytearrayinput, 0, len);
        reportWhileEncrypting(numBlocks, numBlocks);             

        cryptoStream.Close();
        fileInput.Close();
        fileOutput.Close();
    }
    catch (Exception e)
    {
        statusHandler.addStatus("AES Decryption...", statusReport.status.Error, "Error: " + e.Message);
    }
}