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arXiv · 2501.07435

Union: A Trust-minimized Bridge for Rootstock

Ramon Amela·Shreemoy Mishra·Sergio Demian Lerner·Javier Álvarez Cid-Fuentes
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Abstract

We present Union, a trust-minimized bridge protocol that enables secure transfer of BTC between Bitcoin and a secondary blockchain. The growing ecosystem of blockchain systems built around Bitcoin has created a pressing need for secure and efficient bridges to transfer BTC between networks while preserving Bitcoin's security guarantees. Union employs a multi-party variant of BitVMX, an optimistic proving system on Bitcoin, to create a bridge that operates securely under the assumption that at least one participant remains honest. This 1-of-n honest approach is strikingly different from the conventional honest-majority assumption adopted by practically all federated systems. The protocol introduces several innovations: a packet-based architecture that allows security bonds to be reused for multiple bridge operations, improving capital efficiency; a system of enablers to manage functionaries participation and to enforce penalties; a flexible light client framework adaptable to various blockchain architectures; and an efficient stop watch mechanism to optimize time-lock management. Union is a practical and scalable solution for Bitcoin interoperability that maintains strong security guarantees and minimizes trust assumptions.

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Ramon Amela, Shreemoy Mishra, Sergio Demian Lerner, Javier Álvarez Cid-Fuentes. 2025-01-13. Union: A Trust-minimized Bridge for Rootstock. https://arxiv.org/abs/2501.07435

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