  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.
