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

Performance-Based Analysis of Blockchain Scalability Metric

Cryptocurrencies like Bitcoin and Ethereum, are widely known applications of blockchain technology, have drawn much attention and are largely recognized in recent years. Initially Bitcoin and Ethereum processed 7 and 15 Transactions Per Second (TPS) respectively, whereas VISA and Paypal process 1700 and 193 TPS respectively. The biggest challenge to blockchain adoption is scalability, defined as the capacity to change the block size to handle the growing amount of load. This paper attempts to present the existing scalability solutions which are broadly classified into three layers: Layer 0 solutions focus on optimization of propagation protocol for transactions and blocks, Layer 1 solutions are based on the consensus algorithms and data structure, and Layer 2 solutions aims to decrease the load of the primary chain by implementing solutions outside the chain. We present a classification and comparison of existing blockchain scalability solutions based on performance along with their pros and cons

Decentralized Autonomous Organizations and Decentralized Finance, A Bibliometric and Content Analysis

Decentralized Autonomous Organizations (DAOs) present a new technological advancement that may pose a challenge to traditional organizations in terms of governance and decision-making. DAOs offer a novel approach to organization and collaboration by implementing a decentralized, immutable, and trustless system. These organizations run on blockchain technology through the use of smart contracts, enabling autonomous and self-executing operations. Despite their potential, DAOs still face uncertainties regarding their security, governance, and scalability, among other challenges. To determine research gaps and aid in the successful development of DAOs, this paper conducts a bibliometric and content analysis, which is currently missing from existing literature, to provide structural support for this process. This paper identifies the most significant research streams and influential articles on DAOs, providing a comprehensive overview of the current state of this field. Moreover, it investigates the performance of major Decentralized Finance (DeFi) DAOs in light of these research streams, offering insights into their practical applications and effectiveness. To facilitate future research in this domain, the paper proposes several research questions for each identified research stream. These questions aim to address gaps in the current understanding of DAOs, paving the way for novel research that can contribute to the development and enhancement of this innovative technology

Deconstructing the Blockchain to Approach Physical Limits

Transaction throughput, confirmation latency and confirmation reliability are fundamental performance measures of any blockchain system in addition to its security. In a decentralized setting, these measures are limited by two underlying physical network attributes: communication capacity and speed-of-light propagation delay. Existing systems operate far away from these physical limits. In this work we introduce Prism, a new proof-of-work blockchain protocol, which can achieve 1) security against up to 50% adversarial hashing power; 2) optimal throughput up to the capacity C of the network; 3) confirmation latency for honest transactions proportional to the propagation delay D, with confirmation error probability exponentially small in CD ; 4) eventual total ordering of all transactions. Our approach to the design of this protocol is based on deconstructing the blockchain into its basic functionalities and systematically scaling up these functionalities to approach their physical limits.Comment: Computer and Communications Security, 201

Network Performance Improvements for Low-Latency Anonymity Networks

While advances to the Internet have enabled users to easily interact and exchange information online, they have also created several opportunities for adversaries to prey on users’ private information. Whether the motivation for data collection is commercial, where service providers sell data for marketers, or political, where a government censors, blocks and tracks its people, or even personal, for cyberstalking purposes, there is no doubt that the consequences of personal information leaks can be severe. Low-latency anonymity networks have thus emerged as a solution to allow people to surf the Internet without the fear of revealing their identities or locations. In order to provide anonymity to users, anonymity networks route users’ traffic through several intermediate relays, which causes unavoidable extra delays. However, although these networks have been originally designed to support interactive applications, due to a variety of design weaknesses, these networks offer anonymity at the expense of further intolerable performance costs, which disincentivize users from adopting these systems. In this thesis, we seek to improve the network performance of low-latency anonymity networks while maintaining the anonymity guarantees they provide to users today. As an experimentation platform, we use Tor, the most widely used privacy-preserving network that empowers people with low-latency anonymous online access. Since its introduction in 2003, Tor has successfully evolved to support hundreds of thousands of users using thousands of volunteer-operated routers run all around the world. Incidents of sudden increases in Tor’s usage, coinciding with global political events, confirm the importance of the Tor network for Internet users today. We identify four key contributors to the performance problems in low-latency anonymity networks, exemplified by Tor, that significantly impact the experience of low-latency application users. We first consider the lack of resources problem due to the resource-constrained routers, and propose multipath routing and traffic splitting to increase throughput and improve load balancing. Second, we explore the poor quality of service problem, which is exacerbated by the existence of bandwidth-consuming greedy applications in the network. We propose online traffic classification as a means of enabling quality of service for every traffic class. Next, we investigate the poor transport design problem and propose a new transport layer design for anonymous communication networks which addresses the drawbacks of previous proposals. Finally, we address the problem of the lack of congestion control by proposing an ATM-style credit-based hop-by-hop flow control algorithm which caps the queue sizes and allows all relays to react to congestion in the network. Our experimental results confirm the significant performance benefits that can be obtained using our privacy-preserving approaches

TaiJi: Longest Chain Availability with BFT Fast Confirmation

Most state machine replication protocols are either based on the 40-years-old Byzantine Fault Tolerance (BFT) theory or the more recent Nakamoto's longest chain design. Longest chain protocols, designed originally in the Proof-of-Work (PoW) setting, are available under dynamic participation, but has probabilistic confirmation with long latency dependent on the security parameter. BFT protocols, designed for the permissioned setting, has fast deterministic confirmation, but assume a fixed number of nodes always online. We present a new construction which combines a longest chain protocol and a BFT protocol to get the best of both worlds. Using this construction, we design TaiJi, the first dynamically available PoW protocol which has almost deterministic confirmation with latency independent of the security parameter. In contrast to previous hybrid approaches which use a single longest chain to sample participants to run a BFT protocol, our native PoW construction uses many independent longest chains to sample propose actions and vote actions for the BFT protocol. This design enables TaiJi to inherit the full dynamic availability of Bitcoin, as well as its full unpredictability, making it secure against fully-adaptive adversaries with up to 50% of online hash power

Barracuda: The power of l-polling in proof of stake blockchains

Blockchain is a database of storing sequential events as a chain of blocks consistently across a distributed set of nodes. A fundamental problem in doing so is to decide where to put the next block and who should do it in a Sybil-resistant manner. To solve this problem, typically, a node is elected randomly as a leader to append a new block to the end of a chain stored locally by the leader. Ideally, this should extend the chain of blocks, however in practice, due to network imperfections, the local blockchain of the leader might not be synced entirely, thus resulting in forking, a scenario when a new block is appended in the middle of the blockchain, thus creating a fork. These network imperfections create a structure like a tree rather than a chain, where blocks not part of the main chain are abandoned, thus reducing the system’s efficiency. We propose a new peer-to-peer (P2P) protocol called Barracuda, where the leader polls l − 1 random nodes for their blocktree information before proposing a new block and show that this policy has an effect equivalent to having a network that is l times faster under a stochastic network model inspired by Decker and Wattenhofer (2013). We also show via simulations that Barracuda is robust to several real-world factors in the network model