Distributed immutable ledgers, or blockchains, allow the secure digitization of evidential transactions without relying on a trusted third-party. Evidential transactions involve the exchange of any form of physical evidence, such as money, birth certificate, visas, tickets, etc. Most of the time, evidential transactions occur in the context of complex procedures, called evidential protocols, among physical agents. The blockchain provides the mechanisms to transfer evidence, while smart contracts - programs executing within the blockchain in a decentralized and replicated fashion - allow encoding evidential protocols on top of a blockchain. As a smart contract foregoes trusted third-parties and runs on several machines anonymously, it constitutes a highly critical program that has to be secure and trusted-by-design. While most of the current smart contract languages focus on easy programmability, they do not directly address the need of guaranteeing trust and accountability, which becomes a significant issue when evidential protocols are encoded as smart contracts.

翻译：分布式不可变账本（即区块链）能够在无需依赖可信第三方的前提下，安全地实现证据类交易的数字化。证据类交易涉及货币、出生证明、签证、票据等各类实物证据的交换。此类交易通常发生在物理代理之间复杂的程序化流程（称为证据协议）中。区块链提供了证据传输的机制，而智能合约——以去中心化复制方式在区块链上执行的程序——则允许在区块链上对证据协议进行编码。由于智能合约无需可信第三方且匿名运行在多台机器上，它构成了必须实现安全性与可信设计的高度关键程序。尽管当前多数智能合约语言侧重于易编程性，但它们并未直接解决保障信任与可问责性的需求——当证据协议被编码为智能合约时，这一问题将变得尤为突出。