  Homomorphic encryption is a form of encryption which allows computation to be
carried out on the encrypted data without the need for decryption. The success
of quantum approaches to related tasks in a delegated computation setting has
raised the question of whether quantum mechanics may be used to achieve
information theoretically secure fully homomorphic encryption. Here we show,
via an information localisation argument, that deterministic fully homomorphic
encryption necessarily incurs exponential overhead if perfect security is
required.
