Bitcoin's limited programmability and transaction throughput have historically prevented native Bitcoin from participating in decentralized finance (DeFi) applications. Existing solutions depend on honest-majority thresholds, or centralized custodial entities that introduce significant trust requirements. This paper introduces Bitcoin Smart Accounts (BSA), a novel protocol that enables native Bitcoin to access DeFi through trust-minimized infrastructure while maintaining self-custody of funds. BSA achieves this through a combination of emulated Bitcoin covenants using Partially Signed Bitcoin Transactions (PSBTs) and Taproot scripts, a Trusted Execution Environment (TEE)-based arbitration system, and destination chain smart contracts that enable DeFi platforms to accept self-custodial Bitcoin as collateral without necessitating protocol-level modifications. The setup leverages liquidity secured by the Lombard Security Consortium which provides a twofold advantage: for a DeFi protocol, liquidators rely on fungible assets with deep liquidity to quickly exit positions, while for a depositor, the general trust assumptions of honest majority (m-of-n) are reduced to existential honesty (1-of-k). We present the complete protocol design, including the Bitcoin architecture, the TEE-based arbitration mechanism, and the Smart Account Registry for protocol management. We provide a security analysis that demonstrates the correctness, safety, and availability properties under our trust model. Our design enables native Bitcoin to serve as collateral in lending markets and other DeFi protocols without requiring users to relinquish custody of funds.

翻译：比特币有限的可编程性和交易吞吐量历来阻碍原生比特币参与去中心化金融（DeFi）应用。现有解决方案依赖于诚实多数阈值或引入显著信任要求的中心化托管实体。本文提出比特币智能账户（BSA），一种新型协议，使原生比特币能够通过去信任化基础设施访问DeFi，同时保持资金自我托管。BSA通过结合使用部分签名比特币交易（PSBT）和Taproot脚本模拟的比特币契约、基于可信执行环境（TEE）的仲裁系统，以及使DeFi平台能够接受自我托管比特币作为抵押品而无需协议级修改的目标链智能合约来实现这一目标。该方案利用Lombard安全联盟保障的流动性，提供双重优势：对DeFi协议而言，清算者依靠具有深度流动性的可互换资产快速退出头寸；对存款者而言，诚实多数（m-of-n）的通用信任假设降低为存在性诚实（1-of-k）。我们展示了完整的协议设计，包括比特币架构、基于TEE的仲裁机制以及用于协议管理的智能账户注册表。我们提供的安全分析证明了在信任模型下正确性、安全性和可用性属性。我们的设计使原生比特币能够作为抵押品服务于借贷市场及其他DeFi协议，而无需用户放弃资金托管权。