Computationally-secure and composable remote state preparation. (arXiv:1904.06320v1 [quant-ph])

We introduce a protocol between a classical polynomial-time verifier and a
quantum polynomial-time prover that allows the verifier to securely delegate to
the prover the preparation of certain single-qubit quantum states. The protocol
realizes the following functionality, with computational security: the verifier
chooses one of the observables $Z$, $X$, $Y$, $(X+Y)/\sqrt{2}$,
$(X-Y)/\sqrt{2}$; the prover receives a uniformly random eigenstate of the
observable chosen by the verifier; the verifier receives a classical
description of that state. The prover is unaware of which state he received and
moreover, the verifier can check with high confidence whether the preparation
was successful. The delegated preparation of single-qubit states is an
elementary building block in many quantum cryptographic protocols. We expect
our implementation of "random remote state preparation with verification", a
functionality first defined in (Dunjko and Kashefi 2014), to be useful for
removing the need for quantum communication in such protocols while keeping
functionality. The main application that we detail is to a protocol for blind
and verifiable delegated quantum computation (DQC) that builds on the work of
(Fitzsimons and Kashefi 2018), who provided such a protocol with quantum
communication. Recently, both blind an verifiable DQC were shown to be
possible, under computational assumptions, with a classical polynomial-time
client (Mahadev 2017, Mahadev 2018). Compared to the work of Mahadev, our
protocol is more modular, applies to the measurement-based model of computation
(instead of the Hamiltonian model) and is composable. Our proof of security
builds on ideas introduced in (Brakerski et al. 2018).

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