SoK: Diving into DAG-based Blockchain Systems

Blockchain plays an important role in cryptocurrency markets and technology services. However, limitations on high latency and low scalability retard their adoptions and applications in classic designs. Reconstructed blockchain systems have been proposed to avoid the consumption of competitive transactions caused by linear sequenced blocks. These systems, instead, structure transactions/blocks in the form of Directed Acyclic Graph (DAG) and consequently re-build upper layer components including consensus, incentives, \textit{etc.} The promise of DAG-based blockchain systems is to enable fast confirmation (complete transactions within million seconds) and high scalability (attach transactions in parallel) without significantly compromising security. However, this field still lacks systematic work that summarises the DAG technique. To bridge the gap, this Systematization of Knowledge (SoK) provides a comprehensive analysis of DAG-based blockchain systems. Through deconstructing open-sourced systems and reviewing academic researches, we conclude the main components and featured properties of systems, and provide the approach to establish a DAG. With this in hand, we analyze the security and performance of several leading systems, followed by discussions and comparisons with concurrent (scaling blockchain) techniques. We further identify open challenges to highlight the potentiality of DAG-based solutions and indicate their promising directions for future research.Comment: Full versio

Government procurement polices across the Tasman ; what role played by (preferential) trade agreements?

This paper examines developments in government procurement arrangements across the Tasman to assess the extent to which recent trade, especially preferential agreements, of Australia and New Zealand containing government procurement commitments have contributed to any reform in these policies. It argues that (preferential) trade agreements have had little or no impact on any such reforms, and that in the case of Australia, such commitments have not prevented procurement arrangements from going backwards. Transparent price preferences favouring local content have been largely replaced by hidden and more costly discretionary discriminatory measures. In sharp contrast to Australia, New Zealand seems to have maintained a relatively open and non-discriminatory government procurement regime based not on commitments in trade agreements but rather on unconditional MFN unilateral reforms. The central policy message is trade agreements cannot substitute for unilateral reforms

Emerging Trustworthiness Issues in Distributed Learning Systems

A distributed learning system allocates learning processes onto several workstations to enable faster learning algorithms. Federated Learning (FL) is an increasingly popular type of distributed learning which allows mutually untrusted clients to collaboratively train a common machine learning model without sharing their private/proprietary training data with each other. In this dissertation, we aim to address emerging trustworthiness issues in distributed learning systems, particularly in the field of FL. First, we tackle the issue of robustness in FL and demonstrate its susceptibility by presenting a comprehensive analysis of the various poisoning attacks and defensive aggregation rules proposed in the literature and connecting them under a common framework. To address this issue, we propose Federated Rank Learning (FRL) which reduces the space of client updates from a continuous space of float numbers in standard FL to a discrete space of integer values, limiting the adversary\u27s options for poisoning attacks. Next, we address the privacy concerns in FL, including access privacy and data privacy. An adversarial server in FL gets information about the data distribution of a target client by monitoring either I) local updates that the target submits throughout the FL training or II) the access pattern of the target, which can be privacy sensitive in many real-world scenarios. To preserve access privacy, we design Heterogeneous Private Information Retrieval (HPIR), which allows clients to fetch their specific model parameters from untrusted servers without leaking any information. We believe that HPIR will enable new application scenarios for private distributed learning systems, as well as improve the usability of some of the known applications of PIR. To preserve data privacy, we show that local rankings leak less information about private training data. We conduct a comprehensive investigation on the privacy of rankings in FRL to measure data leakage compared to weight parameter updates in standard FL in presence of the state-of-the-art white-box membership inference attack. Finally, we address the issue of fairness in FL where a single model cannot represent all clients equally due to heterogeneity in their data distributions. To alleviate this issue, we propose Equal and Equitable Federated Learning (E2FL). E2FL produces fair federated learning models by preserving both equity and equality among the participating clients based on learning on parameter rankings where multiple global models are learned so that each group of clients can benefit from their personalized model

Reforming the investment climate : lessons for practitioners

Most people agree that a good investment climate is essential for growth and poverty reduction. Less clear is how to achieve it. Many reforms are complex, involving more than technical design and content. They are both political, facing opposition from organized and powerful groups-and institutionally demanding, cutting across different departments and levels of government. Reform thus requires paying as much attention to understanding the politics and institutional dimensions as to policy substance, which is the goal of this paper. Drawing from more than 25 case studies, it shows that there is no single recipe or"manual"for reform, given diverse contexts and serendipity in any reform effort. But three broad lessons emerge. The first is to recognize and seize opportunities for reform. Crisis and new governments are important catalysts, but so is the competition generated by trade integration and new benchmarking information. The second is to invest early in the politics of reform. Central to this process is using education and persuasion strategies to gain wider acceptance and neutralize opponents. Pilot programs can be valuable for demonstrating the benefits and feasibility of change. And the third is to pay greater attention to implementation and monitoring. This does not require full scale public management reforms. Reformers can draw on private sector change management techniques to revitalize public institutions responsible for implementation. Given the cross-cutting nature of reform, new oversight mechanisms may be needed to monitor and sustain reform. The paper concludes with an emerging checklist for reformers and identifies areas for future work.Enterprise Development&Reform,Children and Youth,Economic Theory&Research,Population Policies,Markets and Market Access