code: async def get_decryption_aes_key(self, key: bytes, material_description: Dict[str, Any]) -> bytes:
          
          if self.private_key is None:
              raise ValueError('Private key not provided during initialisation, cannot decrypt key encrypting key')
  
          plaintext = await self._loop.run_in_executor(None, lambda: (self.private_key.decrypt(key, padding.PKCS1v15())))
  
          return plaintext
docs: Get decryption key for a given S3 object
  
          :param key: Base64 decoded version of x-amz-key
          :param material_description: JSON decoded x-amz-matdesc
          :return: Raw AES key bytes