code: def decrypt(self, cipher_text, iv='', auth_data=None, tag=b''):
          
          if not iv:
              raise ValueError('Missing Nonce')
  
          return self.key.decrypt(iv, cipher_text+tag, auth_data)
docs: Decrypts the data and authenticates the associated_data (if provided).
  
          :param cipher_text: The data to decrypt including tag
          :param iv: Initialization Vector
          :param auth_data: Associated data
          :param tag: Authentication tag
          :return: The original plaintext