A New Framework for Quantum Oblivious Transfer

TL;DR

This paper introduces a novel quantum oblivious transfer framework using a fixed basis approach, enabling simpler, multi-round protocols with security in the quantum random oracle model, and develops new quantum entropy extraction tools.

Contribution

The paper presents a new fixed basis framework for quantum oblivious transfer, enabling simpler protocols with fewer rounds and security proofs in the QROM, along with novel entropy extraction methods.

Findings

Non-interactive random-input bit OT with shared EPR pairs.

Two-round OT protocol secure against malicious receivers.

Three-round OT from BB84 states without entanglement or setup.

Abstract

We present a new template for building oblivious transfer from quantum information that we call the "fixed basis" framework. Our framework departs from prior work (eg., Crepeau and Kilian, FOCS '88) by fixing the correct choice of measurement basis used by each player, except for some hidden trap qubits that are intentionally measured in a conjugate basis. We instantiate this template in the quantum random oracle model (QROM) to obtain simple protocols that implement, with security against malicious adversaries: 1. Non-interactive random-input bit OT in a model where parties share EPR pairs a priori. 2. Two-round random-input bit OT without setup, obtained by showing that the protocol above remains secure even if the (potentially malicious) OT receiver sets up the EPR pairs. 3. Three-round chosen-input string OT from BB84 states without entanglement or setup. This improves upon natural variations of the CK88 template that require at least five rounds. Along the way, we develop technical tools that may be of independent interest. We prove that natural functions like XOR enable seedless randomness extraction from certain quantum sources of entropy. We also use idealized (i.e. extractable and equivocal) bit commitments, which we obtain by proving security of simple and efficient constructions in the QROM.