IEEE Middle East Conference on Communications and Networking (MECOM)

Breakdown of a Bit Commitment Protocol

Anshul Singhal, Janis Nötzel

Published Nov 4, 2025• 0 citations

Abstract

Quantum Bit Commitment (QBC) is a foundational primitive in quantum cryptography, intended to enable secure commitments with strong information-theoretic guarantees. The protocol described in ‘Unconditionally secure multi-party quantum commitment scheme’, [1] published in Quantum information processing, 2018 Springer, uses coherent-state encoding and claims statistical hiding and computational binding. In this work, we identify a fundamental vulnerability in the hiding property of the protocol. Specifically, we demonstrate that an adversarial receiver applies Hadamard transformation to the incoming states, effectively changing the basis to enhance distinguishability between the two received messages. This linear optical strategy enables partial extraction of message without the use of quantum storage or entangled resources. We formally analyze the structure of the protocol and quantify the information leakage by computing the distinguishability between quantum state ensembles associated with different commitments. Our findings indicate that the protocol fails to maintain statistical hiding under general quantum adversarial models, raising concerns about its applicability in settings requiring strong concealment guarantees.

DOI: 10.1109/mecom67453.2025.11439646

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