Robust Relativistic Bit Commitment

TL;DR

This paper introduces a robust relativistic bit commitment protocol with three agents that tolerates communication failures, significantly extending the commitment duration while maintaining security.

Contribution

It proposes a new three-agent scheme for relativistic bit commitment that improves resilience to communication failures and extends commitment time.

Findings

Quadratic improvement in expected sustain time.

Retains security level of original protocols.

Tolerates classical communication failures.

Abstract

Relativistic cryptography exploits the fact that no information can travel faster than the speed of light in order to obtain security guarantees that cannot be achieved from the laws of quantum mechanics alone. Recently, Lunghi et al [Phys. Rev. Lett. 2015] presented a bit commitment scheme where each party uses two agents that exchange classical information in a synchronized fashion, and that is both hiding and binding. A caveat is that the commitment time is intrinsically limited by the spatial configuration of the players, and increasing this time requires the agents to exchange messages during the whole duration of the protocol. While such a solution remains computationally attractive, its practicality is severely limited in realistic settings since all communication must remain perfectly synchronized at all times. In this work, we introduce a robust protocol for relativistic bit commitment that tolerates failures of the classical communication network. This is done by adding a third agent to both parties. Our scheme provides a quadratic improvement in terms of expected sustain time compared to the original protocol, while retaining the same level of security.