CADL: Composable Accountability for Distributed Ledgers

区块链已经从简单的加密货币平台发展成为通用的多用途分布式账本技术（dlt）。如今，不仅仅是银行，整个行业都在探索和利用各种dlt的好处，比如透明度、自动化和去中心化的安全属性。除了传统的区块链之外，还有许多不同的dlt。它们通常是为了克服早期bb0代的缺点而设计的，比如代价高昂的共识或缺少隐私机制。然而，安全研究并没有跟上这种快速发展的步伐，到目前为止，安全研究主要集中在传统的区块链上，比如比特币。区块链的安全特性得到了充分的研究和广泛的理解。然而，dlt的一般类别主要被安全研究人员所忽视，现有的区块链结果并不一定适用于dlt。特别是，问责制的关键安全属性——这是密码学中众所周知的属性——是DLT安全研究的盲点。在问责制中，行为不端的各方可以被不可否认地识别出来。这对于回答欺诈当事人的责任问题和阻止当事人的不当行为至关重要。事实上，问责制通常被非正式地声称是dlt的一种安全属性。然而，非区块链dlt的问责制从未正式确定或得到证实。此外，dlt缺乏问责制的模块化处理，然而，这对于在dlt之上设计和分析复杂系统是必要的。在这个项目中，我们将解决这些问题。我们将正式确定dlt的问责制，并开发一个统一的框架，允许对区块链和dlt进行模块化设计和分析，包括其问责制属性。该框架旨在具有高度灵活性，涵盖广泛的dlt和各种安全属性。为了举例说明我们的框架，我们计划构建第一个可证明安全可靠的公告板。这是以一种基于可问责DLT的模块化方式完成的。这样的公告板在许多应用领域都是至关重要的，例如，包括电子投票、拍卖和多方计算。

Blockchains have evolved from simple cryptocurrency platforms into general multi-purpose distributed ledger technologies (DLTs). Nowadays, not just banks but also the industry is exploring and leveraging benefits of various DLTs, such as transparency, automation, and decentralized security properties. There exists a multitude of different DLTs beyond traditional blockchains. They are often designed to overcome drawbacks of early blockchain generations, such as costly consensus or missing privacy mechanisms.However, security research has not kept up with this rapid development, but has so far been focused on traditional blockchains, such as Bitcoin. Security properties of blockchains are well-studied and widely understood. However, the general class of DLTs is mainly ignored by security researchers and existing blockchain results do not necessarily apply to DLTs. In particular, the crucial security property of accountability — which is a well-known property in cryptography — is a blind spot in DLT security research. In accountable systems misbehaving parties can be identified undeniably. This is crucial to answer liability questions in the case of fraudulent parties and to deter parties from misbehavior. Indeed, accountability is often informally claimed as an intended security property of DLTs. However, accountability has never been formalized or proven for non-blockchain DLTs. Also, a modular treatment of accountability is missing for DLTs, which, however, is necessary to design and analyze complex systems on top of DLTs.In this project, we shall resolve these issues. We will formalize accountability for DLTs and develop a unified framework that allows for the modular design and analysis of blockchains and DLTs, including their accountability properties. This framework is intended to be highly flexible, covering a wide range of DLTs and various security properties.To exemplify our framework, we plan to construct the first provably secure and accountable bulletin board. This is done in a modular way based on an accountable DLT. Such bulletin boards are crucial in many application domains, including, for example, e-voting, auctions, and multi-party computation.