Paper 2019/1237

QFactory: classically-instructed remote secret qubits preparation

Alexandru Cojocaru, Léo Colisson, Elham Kashefi, and Petros Wallden


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.

Note: Full version of the paper accepted to Asiacrypt 2019.

Available format(s)
Cryptographic protocols
Publication info
A major revision of an IACR publication in ASIACRYPT 2019
Classical delegated quantum computationLearning With ErrorsProvable security
Contact author(s)
a d cojocaru @ sms ed ac uk
leo colisson @ ens-paris-saclay fr
ekashefi @ gmail com
petros wallden @ ed ac uk
2019-10-23: received
Short URL
Creative Commons Attribution


      author = {Alexandru Cojocaru and Léo Colisson and Elham Kashefi and Petros Wallden},
      title = {QFactory: classically-instructed remote secret qubits preparation},
      howpublished = {Cryptology ePrint Archive, Paper 2019/1237},
      year = {2019},
      note = {\url{}},
      url = {}
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