Covenants are linguistic primitives that extend the Bitcoin script language, allowing transactions to constrain the scripts of the redeeming ones. Advocated as a way of improving the expressiveness of Bitcoin contracts while preserving the simplicity of the UTXO design, various forms of covenants have been proposed over the years. A common drawback of the existing descriptions is the lack of formalization, making it difficult to reason about properties and supported use cases. In this paper we propose a formal model of covenants, which can be implemented with minor modifications to Bitcoin. We use our model to specify some complex Bitcoin contracts, and we discuss how to exploit covenants to design high-level language primitives for Bitcoin contracts.

中文翻译：

---

比特币契约解除束缚

契约是扩展比特币脚本语言的语言原语，允许交易限制赎回者的脚本。作为一种在保持 UTXO 设计简单性的同时提高比特币合约表达能力的方式，多年来已经提出了各种形式的契约。现有描述的一个共同缺点是缺乏形式化，因此难以推理属性和支持的用例。在本文中，我们提出了一个正式的契约模型，只需对比特币稍加修改即可实现。我们使用我们的模型来指定一些复杂的比特币合约，并讨论如何利用契约来设计比特币合约的高级语言原语。