Robust Relativistic Bit Commitment
This work addresses a specific limitation in cryptographic protocols for secure bit commitment, offering an incremental improvement in robustness for applications requiring reliable communication.
The paper tackles the problem of limited practicality in relativistic bit commitment protocols due to perfect synchronization requirements, by introducing a robust protocol that tolerates communication failures and achieves a quadratic improvement in expected sustain time while maintaining security.
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.