Blockchain Papers

Shuai Han, Shengli Liu, Lin Lyu

No abstract is available for this record.

Jing Chen, Silvio Micali

A distributed ledger is a tamperproof sequence of data that can be publicly accessed and augmented by everyone, without being maintained by a centralized party. Distributed ledgers stand to revolutionize the way a modern society operates. They can secure all kinds of traditional transactions, such as payments, asset transfers and titles, in the exact order in which the transactions occur; and enable totally new transactions, such as cryptocurrencies and smart contracts. They can remove intermediaries and usher in a new paradigm for trust. As currently implemented, however, distributed ledgers scale poorly and cannot achieve their enormous potential. In this paper we propose Algorand, an alternative, secure and efficient distributed ledger. Algorand is permissionless and works in a highly asynchronous environment. Unlike prior implementations of distributed ledgers based on “proof of work,” Algorand dispenses with “miners” and requires only a negligible amount of computation. Moreover, its transaction history “forks” only with negligible probability: that is, Algorand guarantees the finality of a transaction the moment the transaction enters the ledger.

Alessio Meneghetti, Tommaso Parise, Massimiliano Sala, Daniele Taufer

The main problem faced by smart contract platforms is the amount of time and computational power required to reach consensus. In a classical blockchain model, each operation is in fact performed by each node, both to update the status and to validate the results of the calculations performed by others. In this short survey we sketch some state-of-the-art approaches to obtain an efficient and scalable computation of smart contracts. Particular emphasis is given to sharding, a promising method that allows parallelization and therefore a more efficient management of the computational resources of the network.

Andy Amoordon, Henrique Rocha

In this paper, we present Tendermint: a Byzantine Fault Tolerant (BFT) application-based blockchain. We show that Tendermint promotes another perception of blockchain programming. Unlike Ethereum which is a blockchain holding many applications, Tendermint proposes to have one application per blockchain. We discuss the idiosyncrasies of Tendermint and how it could, potentially, ease blockchain programming and improve performance. We finish by showing weaknesses of Tendermint, good practices to adopt to hinder security attacks when handling Tendermint nodes, and some potential adjustments in the IBC protocol - an interoperability protocol designed for Tendermint. Our goal is to introduce Tendermint by showing its main characteristics over traditional blockchain platforms such as Bitcoin or Ethereum.

Junghun Yoo, Youlim Jung, Donghwan Shin, Minhyo Bae · 5 authors

A blockchain is a type of distributed ledger that can record transactions between parties in a verifiable and permanent manner. Each node contains its ledger, and the contents of each ledger are maintained to be the same by a consensus algorithm. It is essential to ensure the safety and liveness of the consensus algorithms in blockchain platforms. The Stellar Consensus Protocol (SCP), which is a consensus algorithm for the Stellar cryptocurrency using the blockchain, is utilized for the federated Byzantine agreement. The quorum configuration is one of the essential factors for ensuring the safety and liveness of the SCP; however, it has been rarely studied. In this study, we model the SCP with timed automata and verify the model using a model checking technique, with the purpose of investigating and evaluating the SCP. Through the modeling and verification of the SCP, we could check whether a certain quorum configuration ensures consensus or not, before execution on an actual network. We present several abstraction techniques that help in coping with the extremely large state space of the SCP model in formal verification. The proposed modeling and verification techniques can be utilized for other consensus protocols of various blockchain platforms using the Byzantine agreement.

Alberto Sonnino, Shehar Bano, Mustafa Al-Bassam, George Danezis

We present a family of replay attacks against sharded distributed ledgers, that target cross-shard consensus protocols, such as the recently proposed Chainspace and Omniledger. They allow an attacker, with network access only, to double-spend or lock resources with minimal efforts. The attacker can act independently without colluding with any nodes, and succeed even if all nodes are honest; most of the attacks can also exhibit themselves as faults under periods of asynchrony. These attacks are effective against both shard-led and client-led cross-shard consensus approaches. Finally, we present Byzcuit - a new cross-shard consensus protocol that is immune to those attacks. We implement a prototype of Byzcuit and evaluate it on a real cloud-based testbed, showing that our defenses impact performance minimally, and overall performance surpasses previous works.

Alberto Sonnino, Shehar Bano, Mustafa Al-Bassam, George Danezis

We present a family of replay attacks against sharded distributed ledgers,\nthat target cross-shard consensus protocols, such as the recently proposed\nChainspace and Omniledger. They allow an attacker, with network access only, to\ndouble-spend or lock resources with minimal efforts. The attacker can act\nindependently without colluding with any nodes, and succeed even if all nodes\nare honest; most of the attacks can also exhibit themselves as faults under\nperiods of asynchrony. These attacks are effective against both shard-led and\nclient-led cross-shard consensus approaches. Finally, we present Byzcuit - a\nnew cross-shard consensus protocol that is immune to those attacks. We\nimplement a prototype of Byzcuit and evaluate it on a real cloud-based testbed,\nshowing that our defenses impact performance minimally, and overall performance\nsurpasses previous works.\n

Maurice Herlihy

The roots of blockchain technologies are deeply interwoven in distributed computing.

Nadi Sarrar

Ethereum clients execute transactions in a sequential order prescribed by the consensus protocol. This is a safe and conservative approach to blockchain transaction processing which forgoes running transactions in parallel even when doing so would be beneficial and safe, e.g., when there is no intersection in the sets of accounts that the transactions read or modify. In this work we study the degree of transaction parallelizability and present results from three different simulations using real Ethereum transaction data. Our simulations demonstrate that notable gains are achievable with parallelization, and suggest that the potential for parallelizability improves as transaction rates increase.

Manuel Zander, Tom Waite, Dominik Harz

Scalability of distributed ledgers is a key adoption factor. As an alternative to blockchain-based protocols, directed acyclic graph (DAG) protocols are proposed with the intention to allow a higher volume of transactions to be processed. However, there is still limited understanding of the behaviour and security considerations of DAG-based systems. We present an asynchronous, continuous time, and multi-agent simulation framework for DAG-based cryptocurrencies. We model honest and semi-honest actors in the system to analyse the behaviour of one specific cryptocurrency, IOTA. Our simulations show that the agents that have low latency and a high connection degree have a higher probability of having their transactions accepted in the network with honest and semi-honest strategies. Last, the simulator is built with extensibility in mind. We are in the process of implementing SPECTRE as well as including malicious agents.

Egor Zuev

Mokka is a partial-synchronous, strong consistent BFT consensus algorithm for reaching the consensus about a certain value in open networks. This algorithm has some common approaches nested from RAFT, but its nature and design make Mokka a better solution for DLT (distributed ledger).

Chenyu Huang, Zeyu Wang, Huangxun Chen, Qiwei Hu · 7 authors

In today's blockchain system, designing a secure and high throughput blockchain on par with a centralized payment system is a difficult task. Sharding is one of the most worthwhile emerging technologies for improving the system throughput while maintain high-security level. However, previous sharding-related designs have two main limitations. First, the security and throughput of their random-based sharding system are not high enough as they did not leverage the heterogeneity among validators. Second, to design an incentive mechanism that promotes cooperation could incur a huge overhead on their system. In this article, we propose RepChain, a reputation-based secure and fast blockchain system via sharding, which also provides high incentive to stimulate node cooperation. RepChain utilizes reputation to explicitly characterize the heterogeneity among the validators and lay the foundation for the incentive mechanism. We propose a new double-chain architecture-a transaction chain and a reputation chain. For the transaction chain, an efficient Raft-based synchronous consensus has been presented. For the reputation chain, the synchronous Byzantine fault tolerance consensus that combines collective signing has been utilized to prevent the attack on both reputation score and the related transaction blocks. It supports a high throughput transaction chain with moderate generation speed. Moreover, we propose a reputation-based sharding and leader selection scheme. To analyze the security of RepChain, we propose a recursive formula to calculate the epoch security within only $\mathcal {O}(km^{2})$ time. Furthermore, we implement and evaluate RepChain on the Amazon Web Service platform. The results show our solution can enhance both throughout and security level of the existing sharding-based blockchain system.

Matthew Black, TingWei Liu, Tommaso Cai

Atomic swaps enable the transfer of value between the cryptocurrencies of various blockchains without the need to trust an intermediary. In this paper, we propose the concept of atomic loans, which utilize atomic swap technology to allow market participants to create overcollateralized debt instruments in a trustless and disintermediated manner. The primary use cases for atomic loans include enabling fiat/stablecoin access for cryptocurrency holders to participate within legacy systems, as well as enabling leverage for margin trading. We also introduce a bidding process for liquidating collateral in the case of default which provides the ability for a more fair distribution of collateral.

Yehonatan Buchnik, Roy Friedman

Blockchains are distributed secure ledgers to which transactions are issued continuously and each block of transactions is tightly coupled to its predecessors. Permissioned blockchains place special emphasis on transactions throughput. In this paper we present FireLedger, which leverages the iterative nature of blockchains in order to improve their throughput in optimistic execution scenarios. FireLedger trades latency for throughput in the sense that in FireLedger the last f + 1 blocks of each node's blockchain are considered tentative, i.e., they may be rescinded in case one of the last f + 1 blocks proposers was Byzantine. Yet, when optimistic assumptions are met, a new block is decided in each communication step, which consists of a proposer that sends only its proposal and all other participants are sending a single bit each. Our performance study demonstrates that in a single Amazon data-center, FireLedger running on 10 mid-range Amazon nodes obtains a throughput of up to 160K transactions per second for (typical Bitcoin size) 512 bytes transactions. In a 10 nodes Amazon geo-distributed setting with 512 bytes transactions, FireLedger obtains a throughput of 30K tps. Moreover, on higher end Amazon machines, FireLedger obtains $20%-600%$ better throughput than state of the art protocols like HotStuff and BFT-SMaRt, depending on the exact configuration.

Udo R. Krieger, Michael Herbert Ziegler, Hendrik Cech

No abstract is available for this record.

Mohammad M. Jalalzai, Golden G. Richard, Costas Busch

No abstract is available for this record.

Jae Min Kim, Jae‐Won Lee, Kyungsoo Lee, Junho Huh

Blockchain which enables decentralization of data based on various consensus mechanisms is considered the leading technology of the next generation. Numerous applications are being proposed to benefit from its immunity against modification and manipulation. However, not many appears as a successful business up to now, except for crypto currencies. High operation cost which is essential for the conventional consensus, is acting as an obstacle to the wide adoption of blockchain applications. In this paper, we introduce a novel blockchain platform based on PoP (Proof of Phone), which lowers the operating cost by imposing high entry cost. We conduct theoretical analysis to show that our proposed platform reduces total cost by up to 98.2% compared to that of conventional blockchain. Our new platform will turn various blockchain applications from theory to practice.

Jiaping Wang, Hao Wang

No abstract is available for this record.

Elaine Shi

No abstract is available for this record.

Rachid Guerraoui, Jingjing Wang

No abstract is available for this record.

Ashley S. McAbee, Murali Tummala, John McEachen

In this paper, the authors review documented problems in military intelligence that appear well suited for improvement via blockchain technology. We review guidance from the literature related to determining blockchain technology applicability and propose a decision aid tailored to military intelligence perspectives. We also propose applying batch queueing theory to enable initial feasibility studies and present analysis toward the first known case study of military intelligence incorporation of blockchain technology, a project reviewing blockchain applicability to an intelligence database that stores geographic locations of units of interest.

Shaochi Cheng, Yuan Gao, Xiang‐Yang Li, Yanchang Du · 6 authors

No abstract is available for this record.

Ashish Rajendra Sai, Andrew Le Gear, Jim Buckley

Attaining consensus with no constraints on the consensus participation is a fundamental feature of decentralized blockchain solutions such as Bitcoin (Nakamoto, 2008) and Ethereum (Buterin et al., 2013). Unrestricted consensus participation removes the possibility of censorship and a potential single point of failure, but this design has led to a new concern: that of centralization. Centralization in decentralized blockchain refers to the concentration of a large portion of computing resources to a select few participants. In this paper, we identify the restriction on new participation as a critical contributor to the centralization of consensus power towards commercial and large-scale entities. We also examine the cause of the indirect restriction on participation and propose a metric to identify the degree of these indirect restrictions. This new metric may be used as a threat indicator to identify the centralization of decentralized blockchain caused by indirect participation restrictions.

Nicholas Stifter, Aljosha Judmayer, Edgar Weippl

No abstract is available for this record.