CADL: Composable Accountability for Distributed Ledgers

• Applicant: Professor Dr. Ralf Küsters
• Subject Area: Security and Dependability, Operating-, Communication- and Distributed Systems
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 459731562

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.

• DFG Programme: Research Grants