code: def getPlainText(self, iv, key, ciphertext):
          
          try:
              cipher = AESCipher(key, iv)
              plaintext = cipher.decrypt(ciphertext)
              if sys.version_info >= (3, 0):
                  return plaintext.decode()
              return plaintext
          except Exception as e:
              raise InvalidMessageException(e)
docs: :type iv: bytearray
          :type key: bytearray
          :type ciphertext: bytearray