Circuit Privacy for Quantum Fully Homomorphic Encryption
We study the problem of enforcing circuit privacy for the homomorphic evaluation of quantum circuits. We present a generic transformation from semi-honest to malicious circuit privacy for quantum fully homomorphic encryption (QFHE). Our compiler assumes minimal structural properties of the underlying QFHE scheme, which are satisfied by recent candidate constructions [Mahadev, FOCS 2018]. Thus we obtain a maliciously circuit private QFHE scheme, assuming the quantum hardness of (a circular variant of) the learning with errors (LWE) problem. This immediately implies the existence of a two-round secure function evaluation protocol for quantum circuits with input-indistinguishable security for the client (holding a quantum state |ψ〉) and unbounded simulation security for the server (evaluating a quantum circuit C). *Max Planck Institute for Security and Privacy