Mike Graf

Abstract

In the past few years blockchains have been a major focus for security research, resulting in significant progress in the design, formalization, and analysis of blockchain protocols. However, the more general class of distributed ledgers, which includes not just blockchains but also prominent non-blockchain protocols, such as Corda and OmniLedger, cannot be covered by the state-of-the-art in the security literature yet. These distributed ledgers often break with traditional blockchain paradigms, such as block structures to store data, system-wide consensus, or global consistency. In this paper, we close this gap by proposing the first framework for defining and analyzing the security of general distributed ledgers, with an ideal distributed ledger functionality at the core of our contribution. This functionality covers not only classical blockchains but also non-blockchain distributed ledgers in a unified way. To illustrate our ledger functionality, we first show that the prominent ideal blockchain functionalities from Badertscher et al. and its privacy preserving derivative from Kerber et al. realize (suitable instantiations of) our functionality, which precisely captures their security properties. This immediately implies that their respective implementations, including Bitcoin, Ouroboros Genesis, and Ouroboros Crypsinous, realize our ideal ledger functionality as well. Secondly, we demonstrate that our ideal ledger functionality is capable of precisely modeling also non-blockchain distributed ledgers by performing the first formal security analysis of such a distributed ledger, namely the prominent Corda protocol. Due to the wide spread use of Corda in the industry, in particular the financial sector, this analysis is of independent interest. These results also illustrate that our ideal ledger functionality not just generalizes the modular treatment of blockchains to distributed ledgers, but moreover helps to unify existing results.

Abstract

In the past few years blockchains have been a major focus for security research, resulting in significant progress in the design, formalization, and analysis of blockchain protocols. However, the more general class of distributed ledgers, which includes not just blockchains but also prominent non-blockchain protocols, such as Corda and OmniLedger, cannot be covered by the state-of-the-art in the security literature yet. These distributed ledgers often break with traditional blockchain paradigms, such as block structures to store data, system-wide consensus, or global consistency. In this paper, we close this gap by proposing the first framework for defining and analyzing the security of general distributed ledgers, with an ideal distributed ledger functionality at the core of our contribution. This functionality covers not only classical blockchains but also non-blockchain distributed ledgers in a unified way. To illustrate our ledger functionality, we first show that the prominent ideal blockchain functionalities from Badertscher et al. and its privacy preserving derivative from Kerber et al. realize (suitable instantiations of) our functionality, which precisely captures their security properties. This immediately implies that their respective implementations, including Bitcoin, Ouroboros Genesis, and Ouroboros Crypsinous, realize our ideal ledger functionality as well. Secondly, we demonstrate that our ideal ledger functionality is capable of precisely modeling also non-blockchain distributed ledgers by performing the first formal security analysis of such a distributed ledger, namely the prominent Corda protocol. Due to the wide spread use of Corda in the industry, in particular the financial sector, this analysis is of independent interest. These results also illustrate that our ideal ledger functionality not just generalizes the modular treatment of blockchains to distributed ledgers, but moreover helps to unify existing results.

Abstract

While accountability is a well-known concept in distributed systems and cryptography, in the literature on blockchains (and, more generally, distributed ledgers) the formal treatment of accountability has been a blind spot: there does not exist a formalization let alone a formal proof of accountability for any blockchain yet. Therefore, in this work we put forward and propose a formal treatment of accountability in this domain. Our goal is to formally state and prove that if in a run of a blockchain a central security property, such as consistency, is not satisfied, then misbehaving parties can be identified and held accountable. Accountability is particularly useful for permissioned blockchains where all parties know each other, and hence, accountability incentivizes all parties to behave honestly. We exemplify our approach for one of the most prominent permissioned blockchains: Hyperledger Fabric in its most common instantiation.

Abstract

While accountability is a well-known concept in distributed systems and cryptography, in the literature on blockchains (and, more generally, distributed ledgers) the formal treatment of accountability has been a blind spot: there does not exist a formalization let alone a formal proof of accountability for any blockchain yet. Therefore, in this work we put forward and propose a formal treatment of accountability in this domain. Our goal is to formally state and prove that if in a run of a blockchain a central security property, such as consistency, is not satisfied, then misbehaving parties can be identified and held accountable. Accountability is particularly useful for permissioned blockchains where all parties know each other, and hence, accountability incentivizes all parties to behave honestly. We exemplify our approach for one of the most prominent permissioned blockchains: Hyperledger Fabric in its most common instantiation.