Paper 2026/933

BitVM3: Efficient Bitcoin Bridges via Garbled Circuits

Abstract

Bitcoin bridges, protocols that lock BTC on Bitcoin and represent it on a secondary system, underpin much of Bitcoin's application layer, yet remain poorly secured. Deployed bridges rely on federated custody with honest-majority assumptions, while BitVM2, the state of the art in trust-minimized bridging, incurs worst-case dispute costs of approximately \$16,000, requiring large operator bonds and deposits that restrict participation to well-capitalized parties. We present BitVM3-BRIDGE, a trust-minimized bridge architecture from Bitcoin to (i) chains with finality certificates, such as Ethereum, and (ii) Bitcoin rollups. Our main contribution is an end-to-end bridge construction that makes trust-minimized Bitcoin bridging practical at scale. The bridge is powered by BitVM3-CORE, a modular abstraction for permissionless off-chain computation on Bitcoin using garbled circuits. In BitVM3-CORE, a challenger evaluates a garbled circuit entirely off-chain and obtains a fraud-proof witness if and only if the operator's claim is incorrect. This paradigm reduces total on-chain costs to approximately \$9, with the challenge transaction itself costing just \$0.20. This nearly 1000× cost reduction enables smaller bonds, broader operator participation, and smaller deposit sizes. Beyond the bridge itself, we make two additional contributions. First, we formalize BitVM3-CORE as a sound and complete on-chain proof system under standard cryptographic assumptions. Prior GC-based proposals typically provide either informal security arguments or construction-specific formalizations; by contrast, our framework captures existing constructions within a uniform model and gives a generic treatment based on axiomatized security and functional assumptions. Second, we introduce an on-chain Bitcoin light client secure in the variable-difficulty setting, enabling permissionless chain introspection on Bitcoin and thereby the rollup variant of BitVM3-BRIDGE.