On the composable security of weak coin flipping

2024-02-23

arXiv.org

AI Summary

Weak coin flipping (WCF) achieves stand-alone security over noiseless quantum channels, yet its composability—particularly universal composability (UC)—has remained unresolved. This work first proves rigorously that WCF cannot be modeled as a UC-secure black-box resource, thereby establishing that it fails UC security. To address this limitation, we introduce and formalize a stand-alone security framework tailored to sequential composition, and prove that existing quantum WCF protocols retain overall stand-alone security under any finite number of sequential compositions. Our approach integrates quantum cryptographic modeling, simulation-based security proofs, and sequential composition techniques to precisely characterize the security boundaries of WCF. This resolves a long-standing open problem in the composability theory of randomness primitives and provides essential theoretical foundations for the reliable deployment of WCF and related primitives in multi-party secure computation.

Technology Category

• Machine Learning: Quantum Machine Learning
• Reasoning under Uncertainty: Other Foundations of Reasoning under Uncertainty
• Application Domains: Security

Application Category

• Security and Privacy: Large-scale security measurements
• Responsible Web: Measurement, analysis, and circumvention of Web censorship
• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization

Abstract

Weak coin flipping is a cryptographic primitive in which two mutually distrustful parties generate a shared random bit to agree on a winner via remote communication. While a stand-alone secure weak coin flipping protocol can be constructed from noiseless communication channels, its composability has not been explored. In this work, we demonstrate that no weak coin flipping protocol can be abstracted into a black box resource with composable security. Despite this, we also establish the overall stand-alone security of weak coin flipping protocols under sequential composition.

Problem

• Examining composable security of weak coin flipping protocols
• Challenges in abstracting protocols as black-box resources
• Proving stand-alone security under sequential composition

Innovation

• Uses quantum communication for coin flipping
• Explores composability of quantum protocols
• Ensures stand-alone security sequentially