I am trying to encrypt and decrypt the file. Using AES methods in a MVC web application. I am able to encrypt file and decrypt only once. If I try for second time it gives me "Padding is invalid and cannot be removed error."
- I have tried almost every combination with different properties of AES properties.
- I have tried using statement for disposing the objects.
- I have tried using FlushFinalBlock() after CryptoStream write.
- I have tried with using AES.Padding to Zero (gives me no error but the file doesnt decrypt ), AES.Padding to None gives me error('Length of the data to encrypt is invalid.'). AES.Padding to PKCS7 gives me error (padding is invalid.)
Please find my code below.
public class EncryptionDecryption
{
// Call this function to remove the key from memory after use for security
[DllImport("KERNEL32.DLL", EntryPoint = "RtlZeroMemory")]
public static extern bool ZeroMemory(IntPtr Destination, int Length);
/// <summary>
/// Creates a random salt that will be used to encrypt your file. This method is required on FileEncrypt.
/// </summary>
/// <returns></returns>
public static byte[] GenerateRandomSalt()
{
byte[] data = new byte[32];
using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
{
// Ten iterations.
for (int i = 0; i < 10; i++)
{
// Fill buffer.
rng.GetBytes(data);
}
}
return data;
}
/// <summary>
/// Encrypts a file from its path and a plain password.
/// </summary>
/// <param name="inputFile"></param>
/// <param name="password"></param>
public static void FileEncrypt(string inputFile, string password)
{
//generate random salt
byte[] salt = GenerateRandomSalt();
//create output file name
using (FileStream fsCrypt = new FileStream(inputFile + ".aes", FileMode.Create))
{
//convert password string to byte arrray
byte[] passwordBytes = System.Text.Encoding.UTF8.GetBytes(password);
//Set Rijndael symmetric encryption algorithm
using (AesManaged AES = new AesManaged())
{
AES.KeySize = 256;
AES.BlockSize = 128;
AES.Padding = PaddingMode.None;
//http://stackoverflow.com/questions/2659214/why-do-i-need-to-use-the-rfc2898derivebytes-class-in-net-instead-of-directly
//"What it does is repeatedly hash the user password along with the salt." High iteration counts.
var key = new Rfc2898DeriveBytes(passwordBytes, salt, 50000);
AES.Key = key.GetBytes(AES.KeySize / 8);
AES.IV = key.GetBytes(AES.BlockSize / 8);
//Cipher modes: http://security.stackexchange.com/questions/52665/which-is-the-best-cipher-mode-and-padding-mode-for-aes-encryption
AES.Mode = CipherMode.CBC;
// write salt to the begining of the output file, so in this case can be random every time
fsCrypt.Write(salt, 0, salt.Length);
using (CryptoStream cs = new CryptoStream(fsCrypt, AES.CreateEncryptor(), CryptoStreamMode.Write))
{
using (FileStream fsIn = new FileStream(inputFile, FileMode.Open))
{
//create a buffer (1mb) so only this amount will allocate in the memory and not the whole file
byte[] buffer = new byte[1048576];
int read;
try
{
while ((read = fsIn.Read(buffer, 0, buffer.Length)) > 0)
{
// Application.DoEvents(); // -> for responsive GUI, using Task will be better!
cs.Write(buffer, 0, read);
}
// Close up
fsIn.Close();
}
catch (Exception ex)
{
Console.WriteLine("Error: " + ex.Message);
}
finally
{
if (!cs.HasFlushedFinalBlock)
cs.FlushFinalBlock();
cs.Close();
fsCrypt.Close();
}
}
}
}
}
}
/// <summary>
/// Decrypts an encrypted file with the FileEncrypt method through its path and the plain password.
/// </summary>
/// <param name="inputFile"></param>
/// <param name="outputFile"></param>
/// <param name="password"></param>
public static void FileDecrypt(string inputFile, string outputFile, string password)
{
byte[] passwordBytes = System.Text.Encoding.UTF8.GetBytes(password);
byte[] salt = new byte[32];
using (FileStream fsCrypt = new FileStream(inputFile, FileMode.Open))
{
fsCrypt.Read(salt, 0, salt.Length);
using (AesManaged AES = new AesManaged ())
{
AES.KeySize = 256;
AES.BlockSize = 128;
var key = new Rfc2898DeriveBytes(passwordBytes, salt, 50000);
AES.Key = key.GetBytes(AES.KeySize / 8);
AES.IV = key.GetBytes(AES.BlockSize / 8);
AES.Padding = PaddingMode.PKCS7;
AES.Mode = CipherMode.CBC;
using (CryptoStream cs = new CryptoStream(fsCrypt, AES.CreateDecryptor(), CryptoStreamMode.Read))
{
using (FileStream fsOut = new FileStream(outputFile, FileMode.Create))
{
int read;
byte[] buffer = new byte[1048576];
try
{
while ((read = cs.Read(buffer, 0, buffer.Length)) > 0)
{
//Application.DoEvents();
fsOut.Write(buffer, 0, read);
//if (!cs.HasFlushedFinalBlock)
cs.FlushFinalBlock();
}
}
catch (CryptographicException ex_CryptographicException)
{
Console.WriteLine("CryptographicException error: " + ex_CryptographicException.Message);
}
catch (Exception ex)
{
Console.WriteLine("Error: " + ex.Message);
}
try
{
cs.Close();
}
catch (Exception ex)
{
Console.WriteLine("Error by closing CryptoStream: " + ex.Message);
}
finally
{
fsOut.Close();
fsCrypt.Close();
}
}
}
}
}
}
}
calling methods Encryption
string password = "ThePasswordToDecryptAndEncryptTheFile";
// For additional security Pin the password of your files
GCHandle gch = GCHandle.Alloc(password, GCHandleType.Pinned);
// Encrypt the file
EncryptionDecryption.FileEncrypt(inputFilePath, password);
// To increase the security of the encryption, delete the given password from the memory !
EncryptionDecryption.ZeroMemory(gch.AddrOfPinnedObject(), password.Length * 2);
gch.Free();
Decryption
GCHandle gch2 = GCHandle.Alloc(password, GCHandleType.Pinned);
// Decrypt the file
EncryptionDecryption.FileDecrypt(encryptedFilePath, outputPath, password);
// To increase the security of the decryption, delete the used password from the memory !
EncryptionDecryption.ZeroMemory(gch2.AddrOfPinnedObject(), password.Length * 2);
gch2.Free();
