کد کردن و دی کد کردن رشته در C#

/// <summary>
/// کد کردن رشته ها
/// </summary>
/// <param name="str"></param>
/// <returns></returns>
public static string Encrypt(this string str)
{
 string strEncrKey = "?pws#m";
 byte[] byKey;
 byte[] IV = { 18, 52, 86, 120, 144, 171, 205, 239 };

 try
 {
 byKey = System.Text.Encoding.UTF8.GetBytes(strEncrKey.Substring(0, 8));
 DESCryptoServiceProvider des = new DESCryptoServiceProvider();
 byte[] inputByteArray = Encoding.UTF8.GetBytes(str);
 MemoryStream ms = new MemoryStream();
 CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(byKey, IV), CryptoStreamMode.Write);
 cs.Write(inputByteArray, 0, inputByteArray.Length);
 cs.FlushFinalBlock();
 return Convert.ToBase64String(ms.ToArray());
 }
 catch (Exception ex)
 {
 return ex.Message;
 }
}
/// <summary>
/// دی کد کردن رشته ها
/// </summary>
/// <param name="str"></param>
/// <returns></returns>
public static string Decrypt(this string str)
{
 string sDecrKey = "?pws#m";
 byte[] byKey;
 byte[] IV = { 18, 52, 86, 120, 144, 171, 205, 239 };

 byte[] inputByteArray;
 // inputByteArray.Length = strText.Length;

 try
 {
 byKey = System.Text.Encoding.UTF8.GetBytes(sDecrKey.Substring(0, 8));
 DESCryptoServiceProvider des = new DESCryptoServiceProvider();
 inputByteArray = Convert.FromBase64String(str);
 MemoryStream ms = new MemoryStream();
 CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(byKey, IV), CryptoStreamMode.Write);
 cs.Write(inputByteArray, 0, inputByteArray.Length);
 cs.FlushFinalBlock();
 System.Text.Encoding encoding = System.Text.Encoding.UTF8;
 return encoding.GetString(ms.ToArray());
 }
 catch (Exception ex)
 {
 return ex.Message;
 }
}

Encrypt:uN3ZxZKd2a4=
Decryp2:123