Practical relativistic bit commitment

TL;DR

This paper explores relativistic protocols for secure bit commitment, introducing a new multi-round scheme that extends commitment duration and demonstrating practical implementation possibilities with hardware on Earth.

Contribution

It revisits classical-communication-based schemes, proves quantum security limitations, and proposes a novel multi-round protocol extending commitment time beyond previous limits.

Findings

Protocol secure against quantum adversaries for limited time

New multi-round scheme extends commitment duration

Implementation demonstrates up to 212 ms commitment on Earth

Abstract

Bit commitment is a fundamental cryptographic primitive in which Alice wishes to commit a secret bit to Bob. Perfectly secure bit commitment between two mistrustful parties is impossible through asynchronous exchange of quantum information. Perfect security is however possible when Alice and Bob each split into several agents exchanging classical information at times and locations suitably chosen to satisfy specific relativistic constraints. In this Letter we first revisit a previously proposed scheme that realizes bit commitment using only classical communication. We prove that the protocol is secure against quantum adversaries for a duration limited by the light-speed communication time between the locations of the agents. We then propose a novel multi-round scheme based on finite-field arithmetic that extends the commitment time beyond this limit, and we prove its security against classical attacks. Finally, we present an implementation of these protocols using dedicated hardware and we show how it could be used to realize commitments of duration ranging up to 212 milliseconds by agents occupying antipodal locations on the Earth.