Coherent-State Quantum Rabin Oblivious Transfer: Security Bounds from Unambiguous State Discrimination

Anshul Singhal, Shahram Dehdashti, Janis Nötzel

Published Sep 14, 2026• 0 citations

Abstract

Abstract We investigate coherent-state implementations of quantum Rabin oblivious transfer (OT) based on unambiguous state discrimination and derive the optimal cheating strategies of a dishonest receiver Bob and sender Alice as functions of the coherent-state amplitude. For Bob, we compare the operational guessing probability with the Helstrom minimum-error bound and identify the parameter regimewhere a genuine quantum advantage arises. For Alice, we analyze optimal cheating under three verification strategies employed by Bob, no testing, statistical monitoring, and full interactive testing, and show that the strongest verification requires entangled probe states. Cheating bounds are obtained for both discrete-variable (DV) and continuous-variable (CV) ancilla encodings, including the case where Alice also attempts to infer Bob’s received bit. We further construct a quantum-optical implementation of the semi classical probabilistic Rabin OT protocol (SC-Rabin OT) along with the fully classical Rabin OT (FC-Rabin OT). These are compared with the coherent-state quantum protocol, demonstrating that in the proposed coherent-state based protocol, while Alice’s capacity to cheat remains identical in both the quantum and classical paradigms, it successfully restricts Bob’s cheating probability below classical limits over experimentally relevant parameter ranges. These results establish a measurable quantum advantage for Rabin OT using only coherent states and unambiguous measurements.

DOI: 10.21203/rs.3.rs-10651387/v1

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