Practical Relativistic Bit Commitment

Area of Science:

• Cryptography
• Quantum Information Science
• Theoretical Computer Science

Background:

• Bit commitment is a foundational cryptographic primitive essential for secure two-party computation.
• Perfectly secure bit commitment is impossible with asynchronous quantum information exchange.
• Relativistic constraints and classical communication offer a path to secure bit commitment.

Purpose of the Study:

• To analyze the security of a classical communication-based bit commitment protocol against quantum adversaries.
• To develop and prove the security of a novel multiround bit commitment scheme.
• To experimentally demonstrate the feasibility of relativistic bit commitment.

Main Methods:

• Revisiting and proving the security of a previously proposed classical communication scheme under relativistic constraints.
• Developing a new multiround bit commitment protocol utilizing finite-field arithmetic.
• Implementing the protocols with dedicated hardware and conducting experimental tests.

Main Results:

• The revisited classical protocol is secure against quantum adversaries for a duration limited by light-speed communication.
• The novel multiround scheme extends commitment time beyond the light-speed limit and is secure against classical attacks.
• A 2 ms bit commitment was demonstrated over 131 km, with potential for 212 ms using antipodal Earth locations.

Conclusions:

• Classical communication, combined with relativistic constraints, enables secure bit commitment.
• The proposed multiround scheme offers enhanced commitment times and practical security.
• Experimental validation confirms the viability of relativistic bit commitment for future secure communication systems.