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