title: Practical Relativistic Bit Commitment.
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 an 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 [C. Crépeau et al., Lect. Notes Comput. Sci. 7073, 407 (2011)] 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 multiround 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 demonstrate a 2 ms-long bit commitment over a distance of 131 km. By positioning the agents on antipodal points on the surface of Earth, the commitment time could possibly be extended to 212 ms.
authors.affiliation: Group of Applied Physics, University of Geneva, Chemin de Pinchat 22, CH-1211 Genève 4, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Lunghi
authors.affiliation: Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543, Singapore.|QuTech, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: Kaniewski
authors.affiliation: Group of Applied Physics, University of Geneva, Chemin de Pinchat 22, CH-1211 Genève 4, Switzerland.
authors.forename: F
authors.initials: F
authors.lastname: Bussières
authors.affiliation: Group of Applied Physics, University of Geneva, Chemin de Pinchat 22, CH-1211 Genève 4, Switzerland.
authors.forename: R
authors.initials: R
authors.lastname: Houlmann
authors.affiliation: Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543, Singapore.|School of Physics, The University of Sydney, Sydney 2006, Australia.
authors.forename: M
authors.initials: M
authors.lastname: Tomamichel
authors.affiliation: Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543, Singapore.|QuTech, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.
authors.forename: S
authors.initials: S
authors.lastname: Wehner
authors.affiliation: Group of Applied Physics, University of Geneva, Chemin de Pinchat 22, CH-1211 Genève 4, Switzerland.
authors.forename: H
authors.initials: H
authors.lastname: Zbinden