Blockchain Papers

Xinxin Fan, Qi Chai, Zhi Zhong

No abstract is available for this record.

Xiwei Xu, H. M. N. Dilum Bandara, Qinghua Lu, Dawen Zhang · 5 authors

No abstract is available for this record.

İrshad Hussaın, Özlem Çakır

Blockchain, which is also called a distributed ledger technology (DLT), is an emerging and ever advancing technology having flourishing potential for nourishing and revolutionizing higher education. It stems in decentralization and distributed learning with characteristics of permanence of records, pursuit and transfer of knowledge, authority of institutions, and reliability of teaching and learning. These characteristics of blockchain attract educational institutions particularly the higher education institutions to adopt it. However, in spite of all potential and benefits of blockchain technology, the higher education stakeholders currently seem to be less aware of the social benefits and educational/instructional potential of blockchain technology. It can be addressed through proper advocacy and campaign. The complete chapter will demonstrate possibilities of blockchain technologies in higher education along with its issues and challenges.

Qianwen Wang, Jiehua Huang, Shen Wang, Yibo Chen · 6 authors

Abstract A blockchain is a decentralized distributed public database. It does not have a central authority to maintain this public database by running a cryptographic protocol with distributed nodes. Bitcoin is currently the hottest item in the blockchain, and the Bitcoin node can verify the transaction content and package it into the block. The blockchain guarantees the consistency of the books through the underlying consensus agreement. These consensus algorithms are different because the algorithm security assumptions are different from the actual requirements. This paper sorts and compares various blockchain consensus algorithms, sorts out the development based on blockchain consensus, and points out the advantages and disadvantages of various algorithms, and proposes the development direction of blockchain consensus algorithm. CCS Concepts •Anonymity and privacy issues and measures to enhance them➝Consensus protocols for blockchains

Ronald Doku, Danda B. Rawat, Moses Garuba, Laurent Njilla

Named Data Network's (NDN) data-centric approach makes it a suitable solution in a networking scenario where there are connectivity issues as a result of the dynamism of the network. Coupling of this ability with the blockchain's well-documented immutable trustworthy-distributed ledger feature, the union of blockchain and NDN in an Internet-of-Battlefield-Things (IoBT) setting could prove to be the ideal alliance that would guarantee data exchanged in an IoBT environment is trusted and less susceptible to cyber-attacks and packet losses. Various blockchain technologies, however, require that each node has a ledger that stores information or transactions in a chain of blocks. This poses an issue as nodes in an IoBT setting have varying computing and storage resources. Moreover, most of the nodes in the IoT/IoBT network are plagued with limited resources. As such, there needs to be an approach that ensures that the limited resources of these nodes are efficiently utilized. In this paper, we investigate an approach that merges blockchain and NDN to efficiently utilize the resources of these resource-constrained nodes by only storing relevant information on each node's ledger. Furthermore, we propose a sharding technique called an Interest Group and introduce a novel consensus mechanism called Proof of Common Interest. Performance of the proposed approach is evaluated using numerical results.

Nabil Alkeilani Alkadri, Rachid El Bansarkhani, Johannes Buchmann

A canonical identification (CID) scheme is a 3-move protocol consisting of a commitment, challenge, and response. It constitutes the core design of many cryptographic constructions such as zero-knowledge proof systems and various types of signature schemes. Unlike number-theoretic constructions, CID in the lattice setting usually forces provers to abort and repeat the whole authentication process once the distribution of the computed response does not follow a target distribution independent from the secret key. This concept has been realized by means of rejection sampling, which makes sure that the secrets involved in a protocol are concealed after a certain number of repetitions. This however has a negative impact on the efficiency of interactive protocols because it leads to a number of communication rounds that is multiplicative in the number of aborting participants (or rejection sampling procedures). In this work we show how the CID scheme underlying many lattice-based protocols can be designed with smaller number of aborts or even without aborts. Our new technique exploits (unbalanced) binary hash trees and thus significantly reduces the communication complexity. We show how to apply this new method within interactive zero-knowledge proofs. We also present BLAZE \(^{+}\): a further application of our technique to the recently proposed lattice-based blind signature scheme BLAZE (FC’20). We show that BLAZE \(^{+}\) has an improved performance and communication complexity compared to BLAZE while preserving the size of keys and signatures.

Cosimo Laneve, Adele Veschetti

We study Nakamoto’s Bitcoin protocol that implements a distributed ledger on peer-to-peer asynchronous networks. In particular, we define a principled formal model of key participants - the miners - as stochastic processes and describe the whole system as a parallel composition of miners. We therefore compute the probability that ledgers turn into a state with more severe inconsistencies, e.g. with longer forks, under the assumptions that messages are not lost and nodes are not hostile. We also study how the presence of hostile nodes mining blocks in wrong positions impacts on the consistency of the ledgers. Our theoretical results agree with the simulations performed on a probabilistic model checker that we extended with dynamic datatypes in order to have a faithful description of miners' behaviour.

Joël Gugger

No abstract is available for this record.

Roman Mühlberger, Stefan Bachhofner, Eduardo Castelló Ferrer, Claudio Di Ciccio · 7 authors

Blockchain has evolved into a platform for decentralized applications, with beneficial properties like high integrity, transparency, and resilience against censorship and tampering. However, blockchains are closed-world systems which do not have access to external state. To overcome this limitation, oracles have been introduced in various forms and for different purposes. However so far common oracle best practices have not been dissected, classified, and studied in their fundamental aspects. In this paper, we address this gap by studying foundational blockchain oracle patterns in two foundational dimensions characterising the oracles: (i) the data flow direction, i.e., inbound and outbound data flow, from the viewpoint of the blockchain; and (ii) the initiator of the data flow, i.e., whether it is push or pull-based communication. We provide a structured description of the four patterns in detail, and discuss an implementation of these patterns based on use cases. On this basis we conduct a quantitative analysis, which results in the insight that the four different patterns are characterized by distinct performance and costs profiles.

Christian Sturm, Stefan Jablonski

No abstract is available for this record.

Massimo Bartoletti, Stefano Lande, Roberto Zunino

Covenants are linguistic primitives that extend the Bitcoin script language, allowing transactions to constrain the scripts of the redeeming ones. Advocated as a way of improving the expressiveness of Bitcoin contracts while preserving the simplicity of the UTXO design, various forms of covenants have been proposed over the years. A common drawback of the existing descriptions is the lack of formalization, making it difficult to reason about properties and supported use cases. In this paper we propose a formal model of covenants, which can be implemented with minor modifications to Bitcoin. We use our model to specify some complex Bitcoin contracts, and we discuss how to exploit covenants to design high-level language primitives for Bitcoin contracts.

Amani Altarawneh, Tom Herschberg, Sai Medury, Farah Kandah · 5 authors

Consensus algorithms in distributed systems have attracted much attention in recent studies. However, there is a need for a classification that leads to better understanding and helps direct the deployment of such algorithms. In this paper, we classify common consensus algorithms based on how they decide the order of system state changes. We then determine the extent to which each category prioritizes scalability, decentralization, and security. As with other engineering design scenarios, this is a choose-two tradeoff. Our key contribution is that, based on this taxonomy of tradeoffs, we are able to discern the types of consensus algorithms that work well within the application area(s) for a given distributed system. We find that a dichotomy of algorithms between leader-based and voting-based consensus algorithms emerges from this taxonomy. Applications of this classification scheme include several different categories of distributed ledgers such as blockchains and directed acyclic graphs (DAGs).

Xueping Liang, Sachin Shetty, Peter Foytik, Deepak K. Tosh

Distributed Ledger Technology (DLT) utilizes an architecture that can host a large number of nodes without pre-established trust to provide decentralized services. The blockchain is the most widely used architecture of distributed ledger, where transactions across the whole network are visible to all participants in a chain to prevent tampering. However, transactions may contain sensitive information such as business contract. To secure the system and protect user privacy, we propose a multi-channel architecture that leverages Intel Software Guard Extensions (SGX). We illustrate how SGX capabilities help to defend against attacks on distributed ledgers, by way of SGX enforcement on the participating machines. We adopt the design and implementation of a two layer architecture for securing the blockchain mining process and enhancing the transaction privacy. The security analysis and performance evaluation show that the design and protocols are capable of protecting privacy, defending against adversarial attacks and scalable.

Jetse Brouwer

Distributed ledger technology was expected to spark a technical revolution similar to the internet revolution. After the release of Bitcoin in 2008, many developments have significantly increased the performance of distributed ledger technology. Nevertheless, the first truly scalable ledger has yet to be deployed. All of them have issues with scaling in either the throughput, the number of nodes which can validate transaction or both. The concept behind a distributed ledger is that the integrity of the ledger is a shared responsibility. However, as soon as new technology emerges, also misuse surfaces, especially if there are financial gains involved. The general solution, to prevent such abuse, in distributed ledger technology is through the use of global consensus. If the majority of a network is honest, and we require a majority vote on the validity of a transaction, no malicious transactions will succeed. A downside of requiring a majority vote is that every node eligible to vote must contain full knowledge on all previous transactions. This work argues that the requirement of global consensus is a major limiting factor when it comes to the scalability of current ledgers. The goal of this work is to design a scalable distributed ledger whose security does not rely on global consensus. It proposes a novel algorithm that guarantees security, even under adversarial attack, by up to a third of the network exhibiting byzantine behavior. It does so using Trustchain, a pair-wise ledger designed by the Delft University of Technology, and `Fair Witness Selection Protocol', a newly designed publicly verifiable witness selection algorithm with an indicated message and communication complexity of $O(log^\\star(n))$. A mathematical lower-bound is given on the security level of the algorithm, and the security is reduced to the security of the underlying hash function. Several experiments were executed on the DAS-5 supercomputer to confirm the scalability of this work. These experiments show that the throughput of the network scales linearly, and has been tested up to 2500 nodes (simultaneously acting as validators and clients). To the best of the author's knowledge, it is the only ledger that has no theoretical limits on the number of clients, number of validators, or throughput. A peak-throughput of 7025 tx/s has been observed at a network size of 280 nodes. Furthermore, the total transaction time remained roughly constant at about 15 milliseconds regardless of the network size.

D.S. Popović, C. Avis, M. Byrne, Chong-Soo Cheung · 10 authors

Abstract Insurance industry practitioners have deep knowledge of their industry, but there is a lack of a simple-to-understand, practical blueprint on applying distributed ledger technology solutions, including blockchain. This paper provides a practical guide for actuaries, risk professionals, insurance companies and their Boards on blockchain, including an education piece to provide an understanding of the technology. Examples of real-world applications and use cases in insurance are provided to illustrate the capability of the technology. The current risks and challenges in adopting the technology are also considered. Finally, a checklist of issues to consider in adopting a blockchain solution for insurance business problems is provided.

Yepeng Ding, Hiroyuki Satō

Decentralized techniques are becoming crucial and ubiquitous with the rapid advancement of distributed ledger technologies such as the blockchain. Numerous decentralized systems have been developed to address security and privacy issues with great dependability and reliability via these techniques. Meanwhile, formalization and verification of the decentralized systems is the key to ensuring correctness of the design and security properties of the implementation. In this paper, we propose a novel method of formalizing and verifying decentralized systems with a kind of extended concurrent separation logic. Our logic extends the standard concurrent separation logic with new features including communication encapsulation, environment perception, and node-level reasoning, which enhances modularity and expressiveness. Besides, we develop our logic with unitarity and compatibility to facilitate implementation. Furthermore, we demonstrate the effectiveness and versatility of our method by applying our logic to formalize and verify critical techniques in decentralized systems including the consensus mechanism and the smart contract.

Manuel M. T. Chakravarty, James Chapman, Kenneth MacKenzie, Orestis Melkonian · 8 authors

No abstract is available for this record.

Víctor Pérez, Maximiliano Klemen, Pedro López-García, José F. Morales · 5 authors

No abstract is available for this record.

Lara Mauri, Stelvio Cimato, Ernesto Damiani

Distributed ledger technology is envisioned as one of the cornerstones of promising solutions for building the next generation of critical applications.However, there is still quite a bit of confusion and hype around the real security guarantees this technology offers.This is especially due to the fact that for the vast majority of existing blockchain-based consensus protocols it is really hard to find sufficiently detailed documentation that fully captures their behavior.A number of recent papers have formalized the behavior of Bitcoin-like protocols in order to rigorously study the security and privacy properties of their underlying structure, but surprisingly very little work has been devoted to the formalization of distributed ledger systems using BFTlike approaches.In this work, we focus on XRP Ledger, better known as Ripple, and take the first steps towards the complete formalization of its consensus protocol.To this end, we have investigated all the existing documentation and analyzed its source code.We present a formal description of its consensus protocol for every step.Furthermore, we provide an accurate view of its security guarantees in terms of safety and liveness and show how to increase the desired tolerance by changing the value of specific protocol parameters.

Juan A. Garay, Aggelos Kiayias, Rafail Ostrovsky, Giorgos Panagiotakos · 5 authors

No abstract is available for this record.

Haibo Tian, Huizhi Lin, Fangguo Zhang

No abstract is available for this record.

Jonathan H. Clark

Distributed ledger technology (DLT) stands to benefit industries such as financial services with transparency and censorship resistance. DLT systems need to be scalable to handle mass user adoption. Mass user adoption is required to demonstrate the true value of DLT. This dissertation first analyses scalability in ethereum and EOS. Currently, ethereum 1.0 uses proof of work (PoW) and handles only 14 transactions per second (tps) compared to Visa's peak 47 000 tps. Ethereum 2.0, known as Serenity, introduces sharding, proof of stake (Casper), plasma and state channels in and effort to scale the system. EOS uses a delegated proof of stake (DPoS) protocol, where 21 super-nodes, termed ‘block producers' (BPs), facilitate consensus, bringing about significant scalability improvements (4000 tps). The trade-off is decentralisation. EOS is not sufficiently decentralised because the BPs yield significant power, but are not diverse. This dissertation conducts an empirical analysis using unsupervised machine learning to show that there is a high probability collusion is occurring between certain BPs. It then suggests possible protocol alterations such as inverse vote weighting that could curb adverse voting behaviour in DPoS. It further analyses whether universities are suitable BP's before mapping out required steps for universities to become block producers (leading to improved decentralisation in EOS)

Matthias Fitzi, Peter Gaži, Aggelos Kiayias, Alexander Russell

No abstract is available for this record.

Antoni Olivé

No abstract is available for this record.