QFactory: Classically-Instructed Remote Secret Qubits Preparation

  • Alexandru CojocaruEmail author
  • Léo Colisson
  • Elham Kashefi
  • Petros Wallden
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 11921)


The functionality of classically-instructed remotely prepared random secret qubits was introduced in (Cojocaru et al. 2018) as a way to enable classical parties to participate in secure quantum computation and communications protocols. The idea is that a classical party (client) instructs a quantum party (server) to generate a qubit to the server’s side that is random, unknown to the server but known to the client. Such task is only possible under computational assumptions. In this contribution we define a simpler (basic) primitive consisting of only BB84 states, and give a protocol that realizes this primitive and that is secure against the strongest possible adversary (an arbitrarily deviating malicious server). The specific functions used, were constructed based on known trapdoor one-way functions, resulting to the security of our basic primitive being reduced to the hardness of the Learning With Errors problem. We then give a number of extensions, building on this basic module: extension to larger set of states (that includes non-Clifford states); proper consideration of the abort case; and verifiablity on the module level. The latter is based on “blind self-testing”, a notion we introduced, proved in a limited setting and conjectured its validity for the most general case.


Classical delegated quantum computation Learning With Errors Provable security 



LC is very grateful to Céline Chevalier for all the discussions he had with her, and to Antoine Joux for the very pertinent comments. He would also like to give a special thanks to Geoffroy Couteau, Omar Fawzi and Alain Passelègue who gave him great advices concerning security proof methods. AC and PW are very grateful to Atul Mantri, Thomas Zacharias, Yiannis Tselekounis and Vedran Dunjko for very helpful and interesting discussions. The work was supported by the following grants FA9550-17-1-0055, EPSRC grants: EP/N003829/1 and EP/M013243/1, and by the French ANR Project ANR-18-CE39-0015 CryptiQ.


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Copyright information

© International Association for Cryptologic Research 2019

Authors and Affiliations

  • Alexandru Cojocaru
    • 1
    Email author
  • Léo Colisson
    • 2
  • Elham Kashefi
    • 1
    • 2
  • Petros Wallden
    • 1
  1. 1.School of InformaticsUniversity of EdinburghEdinburghUK
  2. 2.Laboratoire d’Informatique de Paris 6 (LIP6)Sorbonne UniversitéParis CEDEX 05France

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