Formalizing and Implementing Distributed Ledger Objects

Abstract

Despite the hype about blockchains and distributed ledgers, formal abstractions of these objects are scarce 1 . To face this issue, in this paper we provide a proper formulation of a distributed ledger object. In brief, we define a ledger object as a sequence of records, and we provide the operations and the properties that such an object should support. Implementation of a ledger object on top of multiple (possibly geographically dispersed) computing devices gives rise to the distributed ledger object. In contrast to the centralized object, distribution allows operations to be applied concurrently on the ledger, introducing challenges on the consistency of the ledger in each participant. We provide the definitions of three well known consistency guarantees in terms of the operations supported by the ledger object:(1) atomic consistency (linearizability), (2) sequential consistency, and (3) eventual consistency. We then provide implementations of distributed ledgers on asynchronous message passing crash-prone systems using an Atomic Broadcast service, and show that they provide eventual, sequential or atomic consistency semantics respectively. We conclude with a variation of the ledger -the validated ledger -which requires that each record in the ledger satisfies a particular validation rule.1. if π is a VL.get p () operation, then the response event of π returns V ,

Byzantine-tolerant Distributed Grow-only Sets: Specification and Applications

“…The Atomic Appends problem was introduced in [10] as a basic interconnection problem among distributed ledgers (DLOs); see Appendix A for basic definitions with respect to DLOs. Informally, Atomic Appends requires that several records must be appended in their corresponding DLOs, so that either all records are appended (each in the appropriate DLO) or none is appended to any DLO.…”

“…Blockchains (as termed by Nakamoto in [18]) or Distributed Ledger Technologies (DLTs) (as used in [10] and [20]) became one of the most trendy data structures following the introduction of crypto-currencies [18] and their recent application in finance and token-economy. Despite their early wide adoption, little was known initially about the fundamental construction and semantic properties of DLTs.…”

“…Despite their early wide adoption, little was known initially about the fundamental construction and semantic properties of DLTs. A number of research groups attempted to provide rigorous definitions to characterise the fundamental properties of DTLs as those used in Bitcoin and beyond [1,10,11]. Among those, Fernández Anta et al [10], was the first to identify and provide a formal definition of a reliable concurrent object, termed Distributed Ledger Object (DLO), which conveys the essential building block for many DLTs.…”

“…A number of research groups attempted to provide rigorous definitions to characterise the fundamental properties of DTLs as those used in Bitcoin and beyond [1,10,11]. Among those, Fernández Anta et al [10], was the first to identify and provide a formal definition of a reliable concurrent object, termed Distributed Ledger Object (DLO), which conveys the essential building block for many DLTs. In particular, a DLO maintains a sequence of records, and supports two basic operations: append and get.…”

“…The append operation is used to add a new record at the end of the sequence, while the get operation returns the whole sequence. Implementations of DLOs under client and server crashes were proposed in [10], and under Byzantine failures in [6].…”