Quantum Secure Function Evaluations with Real-world Devices
J. van Mil (TU Delft - Applied Sciences)
S.D.C. Wehner – Mentor (TU Delft - QID/Wehner Group)
R.K. Senthoor – Mentor (TU Delft - QID/Wehner Group)
Eliska Greplova – Graduation committee member (TU Delft - QCD/Greplova Lab)
F. Horta Ferreira da Silva – Graduation committee member (TU Delft - BUS/Quantum Delft)
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Abstract
Cryptographic primitives such as Bit Commitment (BC) and Oblivious Transfer (OT) are foundational building blocks for two-party Secure Function Evaluations. While unconditional security for BC is impossible in the quantum setting, it can be realised under additional physical assumptions. In particular, the bounded- and noisy-storage models provide a framework where security is guaranteed against adversaries with limited quantum memory. Recent work by Ribeiro and Wehner [1] introduced the first Measurement-Device-Independent (MDI) protocols for BC and OT in the bounded storage model. For the BC protocols, they consider a variant of BC that is called Randomised String Commitment (RSC). They give two MDI-RSC protocols using polarisation-encoded photon sources: one with perfect single-photon emission and another with multi-photon emissions. They also give an MDI-OT protocol using sources with perfect single-photon emission. However, the MDI security for OT using sources with multi-photon emissions remains an open problem.
This thesis investigates the feasibility of MDI-RSC protocols using sources with multi-photon emissions, such as weak coherent pulses (WCP) and spontaneous parametric down-conversion (SPDC) sources. First, we correct a practical error in the existing MDI-RSC protocol by bounding the relevant parameters, ensuring the validity of the original security claims. Second, we analyse the achievable committed string rates while using WCP and SPDC sources. We further consider heralded SPDC sources, which in principle enable single-photon emission, and discuss the impact of imperfect local detectors on their performance and the consequences that has on the protocol implementation. Finally, motivated by techniques from Twin-Field Quantum Key Distribution (TF-QKD), we give a phase-encoded MDI-RSC protocol using coherent states and provide a sketch of the security proof in the bounded-storage model. We also investigate extending the approach to OT. However, this is still a challenge due to the basis-dependent information leakage inherent in phase-encoded coherent states.