[Paper Review] Fault-Tolerant Distributed Implementation of Digital Social Contracts.

Ouri Poupko, Ehud Shapiro+1 more|arXiv (Cornell University)|Jun 1, 2020

Blockchain Technology Applications and Security13 references4 citations

TL;DR

This paper proposes a fault-tolerant, peer-to-peer distributed ledger architecture for digital social contracts that uses blockchain-per-person, partial ordering, local replication, and cryptographic-signed speech acts. It achieves resilience to faulty agents through a self-sufficient, environmentally friendly, and egalitarian design that eliminates centralized validators and energy-intensive consensus mechanisms.

ABSTRACT

A companion paper defined the notion of digital social contracts, presented a design for a social-contracts programming language, and demonstrated its potential utility via example social contracts. The envisioned setup consists of people with genuine identifiers, which are unique and singular cryptographic key pairs, that operate software agents thus identified on their mobile device. The abstract model of digital social contracts consists of a transition system specifying concurrent, non-deterministic asynchronous agents that operate on a shared ledger by performing digital speech acts, which are cryptographically-signed sequentially-indexed digital actions. Here, we address the distributed-ledger implementation of digital social contracts in the presence of faulty agents: we present a design of a fault-tolerant distributed-ledger transition system and show that it implements the abstract shared-ledger model of digital social contracts, and discuss its resilience to faulty agents. The result is a novel ledger architecture that is distributed with a blockchain-per-person (as opposed to centralized with one blockchain for all), partially-ordered (as opposed to totally-ordered), locally-replicated (as opposed to globally-replicated), asynchronous (as opposed to globally-synchronized), peer-to-peer with each agent being both an actor and a validator (as opposed to having dedicated miners, validators, and clients), environmentally-friendly (as opposed to the environmentally-harmful Proof-of-Work), self-sufficient (as opposed to the energy-hogging Proof-of-Work or capital-hogging Proof-of-Stake) and egalitarian (as opposed to the plutocratic Proof-of-Work and Proof-of-Stake).

Motivation & Objective

• To design a distributed ledger system that correctly implements the abstract model of digital social contracts under faulty agent conditions.
• To ensure resilience against faulty or malicious agents in a decentralized, peer-to-peer environment.
• To eliminate reliance on energy-intensive or capital-intensive consensus mechanisms like Proof-of-Work or Proof-of-Stake.
• To support asynchronous, non-deterministic, and concurrent agent interactions via cryptographically-signed speech acts on a shared ledger.
• To achieve a self-sufficient, environmentally sustainable, and egalitarian system where every agent acts as both validator and participant.

Proposed method

• Designs a distributed-ledger transition system that models digital social contracts as a concurrent, non-deterministic, asynchronous transition system.
• Uses cryptographically-signed, sequentially-indexed digital speech acts as atomic actions on a shared ledger to represent agent interactions.
• Employs a blockchain-per-person architecture, where each agent maintains its own local blockchain for transaction ordering and validation.
• Applies partial ordering of transactions across agents to allow flexible, asynchronous coordination without global synchronization.
• Enables each agent to act as both a validator and a participant, eliminating dedicated mining or validation roles.
• Relies on cryptographic key pairs for unique, verifiable identities and ensures fault tolerance through consensus mechanisms resilient to Byzantine faults.

Experimental results

Research questions

• RQ1 How can a distributed ledger be designed to correctly implement the abstract model of digital social contracts in the presence of faulty agents?
• RQ2 What architectural principles enable a ledger to be both fault-tolerant and self-sufficient without relying on energy- or capital-intensive consensus?
• RQ3 How can a system maintain consistency and security in an asynchronous, peer-to-peer environment with no central authority?
• RQ4 In what ways does a blockchain-per-person, locally replicated ledger improve resilience and sustainability compared to global blockchains?
• RQ5 How can digital social contracts be implemented using cryptographically-signed, sequentially-indexed speech acts in a decentralized and fault-tolerant manner?

Key findings

• The proposed ledger architecture successfully implements the abstract shared-ledger model of digital social contracts in a fault-tolerant manner.
• The system achieves resilience to faulty agents through a combination of local replication, partial ordering, and cryptographic verification of speech acts.
• The blockchain-per-person model eliminates the need for global synchronization and reduces attack surface and resource overhead.
• The design is environmentally sustainable by avoiding energy-intensive consensus mechanisms like Proof-of-Work.
• The system is self-sufficient and egalitarian, as every agent contributes to validation without requiring external capital or energy investment.
• The architecture supports secure, concurrent, and non-deterministic agent interactions via cryptographically-signed digital speech acts on a shared, distributed ledger.