Aes decryption in c#

gistfile1.txt

public static string DecryptStringFromBytes(string cipherTextString, string KeyString, string IVString)
            {
                var Key = Convert.FromBase64String(KeyString);
                var IV = Convert.FromBase64String(IVString);
                var cipherText = Convert.FromBase64String(cipherTextString);

                // Check arguments.
                if (cipherText == null || cipherText.Length <= 0)
                    throw new ArgumentNullException("cipherText");
                if (Key == null || Key.Length <= 0)
                    throw new ArgumentNullException("Key");
                if (IV == null || IV.Length <= 0)
                    throw new ArgumentNullException("IV");

                // Declare the string used to hold
                // the decrypted text.
                string plaintext = null;

                // Create an RijndaelManaged object
                // with the specified key and IV.
                using (RijndaelManaged rijAlg = new RijndaelManaged())
                {
                    rijAlg.Key = Key;
                    rijAlg.IV = IV;

                    // Create a decryptor to perform the stream transform.
                    ICryptoTransform decryptor = rijAlg.CreateDecryptor(rijAlg.Key, rijAlg.IV);

                    // Create the streams used for decryption.
                    using (MemoryStream msDecrypt = new MemoryStream(cipherText))
                    {
                        using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
                        {
                            using (StreamReader srDecrypt = new StreamReader(csDecrypt))
                            {
                                // Read the decrypted bytes from the decrypting stream
                                // and place them in a string.
                                plaintext = srDecrypt.ReadToEnd();
                            }
                        }
                    }
                }

                return plaintext;
            }