Security Limitations of Classical-Client Delegated Quantum Computing

Christian Badertscher, Alexandru Cojocaru, Leo Colisson, Elham Kashefi, Dominik Leichtle, Atul Mantri, Petros Wallden

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Secure delegated quantum computing allows a computationally weak client to outsource an arbitrary quantum computation to an untrusted quantum server in a privacy-preserving manner. One of the promising candidates to achieve classical delegation of quantum computation is classical-client remote state preparation (RSP_CC), where a client remotely prepares a quantum state using a classical channel. However, the privacy loss incurred by employing RSP_CC as a sub-module is unclear.

In this work, we investigate this question using the Constructive Cryptography framework by Maurer and Renner (ICS'11). We first identify the goal of RSP_CC as the construction of ideal RSP resources from classical channels and then reveal the security limitations of using RSP_CC. First, we uncover a fundamental relationship between constructing ideal RSP resources (from classical channels) and the task of cloning quantum states. Any classically constructed ideal RSP resource must leak to the server the full classical description (possibly in an encoded form) of the generated quantum state, even if we target computational security only. As a consequence, we find that the realization of common RSP resources, without weakening their guarantees drastically, is impossible due to the no-cloning theorem. Second, the above result does not rule out that a specific RSP_CC protocol can replace the quantum channel at least in some contexts, such as the Universal Blind Quantum Computing (UBQC) protocol of Broadbent et al. (FOCS '09). However, we show that the resulting UBQC protocol cannot maintain its proven composable security as soon as RSP_CC is used as a subroutine. Third, we show that replacing the quantum channel of the above UBQC protocol by the RSP_CC protocol QFactory of Cojocaru et al. (Asiacrypt '19), preserves the weaker, game-based, security of UBQC.
Original languageEnglish
Title of host publicationAdvances in Cryptology – ASIACRYPT 2020
PublisherSpringer, Cham
Pages667-696
Number of pages30
Volume2
ISBN (Electronic)978-3-030-64834-3
ISBN (Print)978-3-030-64833-6
DOIs
Publication statusPublished - 5 Dec 2020
Event26th Annual International Conference on the Theory and Application of Cryptology and Information Security - Online
Duration: 7 Dec 202011 Dec 2020
https://asiacrypt.iacr.org/2020/

Publication series

Name Lecture Notes in Computer Science
PublisherSpringer
Volume12492
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349

Conference

Conference26th Annual International Conference on the Theory and Application of Cryptology and Information Security
Abbreviated titleASIACRYPT 2020
CityOnline
Period7/12/2011/12/20
Internet address

Keywords

  • Remote State Preparation
  • Blind Quantum Computing

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