Windows Phone - Poor encryption performance - performance

Question

I have used following code for encryption in Windows Phone:
public static string Encrypt(string dataToEncrypt, string password)
{
AesManaged aes = null;
MemoryStream memoryStream = null;
CryptoStream cryptoStream = null;
string salt = "12345678";
try
{
// Generate a Key based on a Password and HMACSHA1 pseudo-random number generator
// Salt must be at least 8 bytes long
// Use an iteration count of at least 1000
Rfc2898DeriveBytes rfc2898 = new Rfc2898DeriveBytes(password, Encoding.UTF8.GetBytes(salt), 10000);
// Create AES algorithm
aes = new AesManaged();
// Key derived from byte array with 32 pseudo-random key bytes
aes.Key = rfc2898.GetBytes(32);
// IV derived from byte array with 16 pseudo-random key bytes
aes.IV = rfc2898.GetBytes(16);
// Create Memory and Crypto Streams
memoryStream = new MemoryStream();
cryptoStream = new CryptoStream(memoryStream, aes.CreateEncryptor(), CryptoStreamMode.Write);
// Encrypt Data
byte[] data = Encoding.UTF8.GetBytes(dataToEncrypt);
cryptoStream.Write(data, 0, data.Length);
cryptoStream.FlushFinalBlock();
// Return Base 64 String
return Convert.ToBase64String(memoryStream.ToArray());
}
finally
{
if (cryptoStream != null)
{
cryptoStream.Close();
}
if (memoryStream != null)
{
memoryStream.Close();
}
if (aes != null)
{
aes.Clear();
}
}
}
public static string Decrypt(string dataToDecrypt, string password)
{
AesManaged aes = null;
MemoryStream memoryStream = null;
string salt = "12345678";
try
{
// Generate a Key based on a Password and HMACSHA1 pseudo-random number generator
// Salt must be at least 8 bytes long
// Use an iteration count of at least 1000
Rfc2898DeriveBytes rfc2898 = new Rfc2898DeriveBytes(password, Encoding.UTF8.GetBytes(salt), 10000);
// Create AES algorithm
aes = new AesManaged();
// Key derived from byte array with 32 pseudo-random key bytes
aes.Key = rfc2898.GetBytes(32);
// IV derived from byte array with 16 pseudo-random key bytes
aes.IV = rfc2898.GetBytes(16);
// Create Memory and Crypto Streams
memoryStream = new MemoryStream();
CryptoStream cryptoStream = new CryptoStream(memoryStream, aes.CreateDecryptor(), CryptoStreamMode.Write);
// Decrypt Data
byte[] data = Convert.FromBase64String(dataToDecrypt);
cryptoStream.Write(data, 0, data.Length);
cryptoStream.FlushFinalBlock();
// Return Decrypted String
byte[] decryptBytes = memoryStream.ToArray();
// Dispose
if (cryptoStream != null)
{
cryptoStream.Dispose();
}
// Retval
return Encoding.UTF8.GetString(decryptBytes, 0, decryptBytes.Length);
}
finally
{
if (memoryStream != null)
{
memoryStream.Dispose();
}
if (aes != null)
{
aes.Clear();
}
}
}
The performance of encyrption is very poor. Can anyone suggest some improvement on above code?

Answer 1

Sure, you could move the key derivation code using Rfc2898DeriveBytes outside of those function since the key for a given password will be constant and will be usually used multiple times. Other than that I don't see much room for improvement.

Answer 2

Perhaps you should introduce some using() brackets to make sure there are no memory leaks. You could have a look at this:
http://zayko.net/post/How-to-EncryptDecrypt-a-String-in-Silverlight-for-Windows-Phone-7.aspx
This would only help if your function became slower over time, instead on the first run.