Rational Fair Consensus in the GOSSIP Model

The \emph{rational fair consensus problem} can be informally defined as follows. Consider a network of $n$ (selfish) \emph{rational agents}, each of them initially supporting a \emph{color} chosen from a finite set $\Sigma$. The goal is to design a protocol that leads the network to a stable monochromatic configuration (i.e. a consensus) such that the probability that the winning color is $c$ is equal to the fraction of the agents that initially support $c$, for any $c \in \Sigma$. Furthermore, this fairness property must be guaranteed (with high probability) even in presence of any fixed \emph{coalition} of rational agents that may deviate from the protocol in order to increase the winning probability of their supported colors. A protocol having this property, in presence of coalitions of size at most $t$, is said to be a \emph{whp\,-$t$-strong equilibrium}. We investigate, for the first time, the rational fair consensus problem in the GOSSIP communication model where, at every round, every agent can actively contact at most one neighbor via a \emph{push$/$pull} operation. We provide a randomized GOSSIP protocol that, starting from any initial color configuration of the complete graph, achieves rational fair consensus within $O(\log n)$ rounds using messages of $O(\log^2n)$ size, w.h.p. More in details, we prove that our protocol is a whp\,-$t$-strong equilibrium for any $t = o(n/\log n)$ and, moreover, it tolerates worst-case permanent faults provided that the number of non-faulty agents is $\Omega(n)$. As far as we know, our protocol is the first solution which avoids any all-to-all communication, thus resulting in $o(n^2)$ message complexity.Comment: Accepted at IPDPS'1

FairLedger: A Fair Blockchain Protocol for Financial Institutions

Financial institutions are currently looking into technologies for permissioned blockchains. A major effort in this direction is Hyperledger, an open source project hosted by the Linux Foundation and backed by a consortium of over a hundred companies. A key component in permissioned blockchain protocols is a byzantine fault tolerant (BFT) consensus engine that orders transactions. However, currently available BFT solutions in Hyperledger (as well as in the literature at large) are inadequate for financial settings; they are not designed to ensure fairness or to tolerate selfish behavior that arises when financial institutions strive to maximize their own profit. We present FairLedger, a permissioned blockchain BFT protocol, which is fair, designed to deal with rational behavior, and, no less important, easy to understand and implement. The secret sauce of our protocol is a new communication abstraction, called detectable all-to-all (DA2A), which allows us to detect participants (byzantine or rational) that deviate from the protocol, and punish them. We implement FairLedger in the Hyperledger open source project, using Iroha framework, one of the biggest projects therein. To evaluate FairLegder's performance, we also implement it in the PBFT framework and compare the two protocols. Our results show that in failure-free scenarios FairLedger achieves better throughput than both Iroha's implementation and PBFT in wide-area settings

Trial By Jury Involving Persons Accused of Terrorism or Supporting Terrorism

This chapter explores issues in jury trials involving persons accused of committing acts of international terrorism or financially or otherwise supporting those who do or may commit such acts. The jury is a unique institution that draws upon laypersons to decide whether a person charged with a crime is guilty or innocent. Although the jury is instructed and guided by a trial judge and procedural rules shape what the jury is allowed to hear, ultimately the laypersons deliberate alone and render their verdict. A basic principle of the jury system is that at the start of trial the jurors should have open minds and regard the accused innocent until proven guilty. The chapter raises issues about jurors\u27 assumptions of innocence in the aftermath of terrorist bombings in the United States, England, Bali, Spain and elsewhere when persons are persons accused of committing acts of terrorism or indirectly supporting terrorists through financing organizations associated with terrorism. A study of a United States trial involving charges of supporting terrorism is used to illustrate the problem, but the thesis of this chapter is that the basic issues apply to trials that might be held in England, Australia, Canada or other countries with jury systems

Trial By Jury Involving Persons Accused of Terrorism or Supporting Terrorism

This chapter explores issues in jury trials involving persons accused of committing acts of international terrorism or financially or otherwise supporting those who do or may commit such acts. The jury is a unique institution that draws upon laypersons to decide whether a person charged with a crime is guilty or innocent. Although the jury is instructed and guided by a trial judge and procedural rules shape what the jury is allowed to hear, ultimately the laypersons deliberate alone and render their verdict. A basic principle of the jury system is that at the start of trial the jurors should have open minds and regard the accused innocent until proven guilty. The chapter raises issues about jurors\u27 assumptions of innocence in the aftermath of terrorist bombings in the United States, England, Bali, Spain and elsewhere when persons are persons accused of committing acts of terrorism or indirectly supporting terrorists through financing organizations associated with terrorism. A study of a United States trial involving charges of supporting terrorism is used to illustrate the problem, but the thesis of this chapter is that the basic issues apply to trials that might be held in England, Australia, Canada or other countries with jury systems

Overview of Polkadot and its Design Considerations

In this paper we describe the design components of the heterogenous multi-chain protocol Polkadot and explain how these components help Polkadot address some of the existing shortcomings of blockchain technologies. At present, a vast number of blockchain projects have been introduced and employed with various features that are not necessarily designed to work with each other. This makes it difficult for users to utilise a large number of applications on different blockchain projects. Moreover, with the increase in number of projects the security that each one is providing individually becomes weaker. Polkadot aims to provide a scalable and interoperable framework for multiple chains with pooled security that is achieved by the collection of components described in this paper

Towards practicalization of blockchain-based decentralized applications

Blockchain can be defined as an immutable ledger for recording transactions, maintained in a distributed network of mutually untrusting peers. Blockchain technology has been widely applied to various fields beyond its initial usage of cryptocurrency. However, blockchain itself is insufficient to meet all the desired security or efficiency requirements for diversified application scenarios. This dissertation focuses on two core functionalities that blockchain provides, i.e., robust storage and reliable computation. Three concrete application scenarios including Internet of Things (IoT), cybersecurity management (CSM), and peer-to-peer (P2P) content delivery network (CDN) are utilized to elaborate the general design principles for these two main functionalities. Among them, the IoT and CSM applications involve the design of blockchain-based robust storage and management while the P2P CDN requires reliable computation. Such general design principles derived from disparate application scenarios have the potential to realize practicalization of many other blockchain-enabled decentralized applications. In the IoT application, blockchain-based decentralized data management is capable of handling faulty nodes, as designed in the cybersecurity application. But an important issue lies in the interaction between external network and blockchain network, i.e., external clients must rely on a relay node to communicate with the full nodes in the blockchain. Compromization of such relay nodes may result in a security breach and even a blockage of IoT sensors from the network. Therefore, a censorship-resistant blockchain-based decentralized IoT management system is proposed. Experimental results from proof-of-concept implementation and deployment in a real distributed environment show the feasibility and effectiveness in achieving censorship resistance. The CSM application incorporates blockchain to provide robust storage of historical cybersecurity data so that with a certain level of cyber intelligence, a defender can determine if a network has been compromised and to what extent. The CSM functions can be categorized into three classes: Network-centric (N-CSM), Tools-centric (T-CSM) and Application-centric (A-CSM). The cyber intelligence identifies new attackers, victims, or defense capabilities. Moreover, a decentralized storage network (DSN) is integrated to reduce on-chain storage costs without undermining its robustness. Experiments with the prototype implementation and real-world cyber datasets show that the blockchain-based CSM solution is effective and efficient. The P2P CDN application explores and utilizes the functionality of reliable computation that blockchain empowers. Particularly, P2P CDN is promising to provide benefits including cost-saving and scalable peak-demand handling compared with centralized CDNs. However, reliable P2P delivery requires proper enforcement of delivery fairness. Unfortunately, most existing studies on delivery fairness are based on non-cooperative game-theoretic assumptions that are arguably unrealistic in the ad-hoc P2P setting. To address this issue, an expressive security requirement for desired fair P2P content delivery is defined and two efficient approaches based on blockchain for P2P downloading and P2P streaming are proposed. The proposed system guarantees the fairness for each party even when all others collude to arbitrarily misbehave and achieves asymptotically optimal on-chain costs and optimal delivery communication

Social Influence and Individual Difference in Experimental Juries

In a jury decision-making, individuals must compromise in order to reach a group consensus. If individuals compromise for non-rational reasons, such as a preference for conformity or due to erroneous information, then the final decision of the group may be biased. This paper presents original experimental data which shows that groups do have a significant tendency to compromise in jury-like settings. Econometric evidence also shows that features of groups, including the generosity of the group overall, will dictate the extent of compromise. The data also reveal that individual traits such as gender and capacity for empathy are associated with the extent of compromise in a jury-type setting. The implications are that interactions between individual and group characteristics limit the objectivity of decision-making

Order Without Judges: Customary Adjudication

Scholarship on custom and law has largely focused on the creation and enforcement of informal rules, demonstrating and in some cases endorsing the existence of order without law. But creating and enforcing rules are only two of the three functions of governance, corresponding roughly with what in other contexts are called the legislative and executive branches. The third function—adjudication—has not played such a prominent role in the scholarly literature on informal governance. As one leading scholar puts it: Custom has no constitution or judges. But if customs can be created and enforced by nonstate actors, why should scholars assume that formal (that is, noncustomary) courts are the only institutions that do or should adjudicate those customs? This Essay seeks to describe and emphasize the role of customary adjudication, the third branch of customary governance. In doing so, it has three main goals: first, to argue that customary governance can be understood in terms of the same three functions familiar to students of formal governance; second, to deliver a preliminary and tentative account of the third of these branches; and finally, to suggest that existing scholarship on custom and law has given comparatively little attention to the functions and forms of customary adjudication. If successful, those contributions should set the stage for future descriptive and normative work