Blockchain Papers

Lukas Aumayr, Oğuzhan Ersoy, Andreas Erwig, Sebastian Faust · 8 authors

No abstract is available for this record.

Eder J. Scheid, Bruno Rodrigues, Christian Killer, Muriel Figueredo Franco · 6 authors

No abstract is available for this record.

Sarah Bouraga

No abstract is available for this record.

Yuhao Dong, Raouf Boutaba

Decentralized cryptocurrencies have gathered increasing interest in the past few years, raising hopes of a new era of non-sovereign electronic money. Unfortunately, cryptocurrencies perform poorly as actual money due to their unacceptably volatile purchasing power. "Stablecoins" aiming to reduce this volatility, on the other hand, tend to peg to an external currency like the US dollar, gravely weakening the decentralization that makes cryptocurrencies so attractive.

Peng Jiang, Baoqi Qiu, Liehuang Zhu, Keke Gai

Internet of Things (IoT) makes great development and gains popularity with a mature combination with cloud computing. Plaintext data can be encrypted when data owners try to secure the confidentiality, while the encrypted data retrieval can be achieved by a cryptographic primitive named searchable encryption. Public-key encryption with keyword search (PEKS) is built on the asymmetric setting, however, the “honest-but-curious” assumption in PEKS creates challenges on the search reliability when malicious behaviors happen. It is nontrivial to enable the reliable search while preserving keyword privacy, as users who have paid need to receive either correct-and-wanted results or compensations. In this work, we apply blockchain to resolve this problem and design SearchBC, a blockchain-based PEKS framework supporting private, reliable, and fair encrypted search over the asymmetric setting. SearchBC is built on top of the blockchain and a keyword server to allow fairness in transactions and keyword preprocessing. We present a SearchBC instantiation and formally prove its security under the newly defined security model. SearchBC guarantees that search operations are fair and reliable and that the used keyword keeps privacy. The implementation results show that SearchBC provides a feasible means with reasonable communication and computation costs.

Matthias Lohr, Benjamin Schlosser, Jan Jürjens, Steffen Staab

Blockchains can guarantee fairness during the exchange of digital goods such that in a two-party exchange no one is defrauded by a malicious opponent. While several notions of fairness have been discussed in the literature, they all ignore that damage cannot only be incurred by the malicious failure of the exchange, but also by an unfair allocation of transaction costs. To address this issue we: 1. define the novel concept of cost fairness, which 2. builds on the notion of maximum cost matrices that formalize transaction costs in different combinations of benevolent and malicious behavior. 3. We show how limited notions of cost fairness can be achieved by modifying an existing exchange protocol or using a container protocol. In particular, we also provide 4. a tool that let us predict the maximum cost matrix for a specific protocol execution and, thus, gives trade exchange parties the possibility to weigh not only the value of transaction of exchanged goods but also the associated transaction costs.

Kaushik Ayinala, Baek-Young Choi, Sejun Song

Blockchain technologies have been rapidly enhanced in recent years. However, its scalability still has limitations in terms of throughput and broadcast delay as the network and the amount of transaction data increase. To improve scalability of blockchain networks, we propose a novel approach named PiChu that accelerates block propagation in blockchain networks by pipelining and verifying chunks of a block in parallel. Accelerating block propagation reduces the mining interval and chance of fork occurring, which in turn increases throughput. Our approach can be applied to the blockchain networks either directly or with a minor modification to the consensus. Through an extensive and large scale simulations, we validate that the proposed PiChu scheme significantly enhances the scalability of blockchain networks. For instance, a 64 MB block can be broadcasted in just 80 seconds in a blockchain network with a million nodes. The efficiency of PiChu broadcasting increases with bigger block sizes and a larger number of nodes in the network.

Philipp Frauenthaler, Marten Sigwart, Christof Spanring, Michael Sober · 5 authors

Current blockchain relay schemes require the immediate validation of each relayed block header by the destination blockchain. This leads to high operating cost when deploying these relays between Ethereum-based blockchains where validating block headers on-chain is computationally expensive.To overcome these limitations, we introduce a novel relay scheme that employs a validation-on-demand pattern combined with economic incentives to reduce the cost of operating a relay between Ethereum-based blockchains by up to 92%. With this relay scheme, decentralized interoperability between blockchains like Ethereum and Ethereum Classic becomes feasible.

Carlos Santiago, Choonhwa Lee

Improving performance of blockchain systems is one of the principal research interests in the field. While many efforts are being made to produce faster and more efficient consensus protocols, they are all constrained by a common factor: the time it takes for a block to propagate through the network. Most blockchain networks use different variations of gossip-like communication protocols to be able to send large messages whilst minimizing latency and bandwidth use. Unfortunately, it still supposes a major bottleneck for state-of-the-art high-performance blockchain systems. In this paper we analyze the most relevant work being done to improve message propagation in blockchain networks. More specifically, we introduce the problem of neighbour selection for gossip protocols, and we propose an alternative method to pick neighbours based on weights derived from self-collected metrics. Our technical performance study shows that the proposed method can suppose an improvement of up to 5 seconds. Additionally, in combination with the use of erasure coding techniques, we are capable of achieving a 75% reduction of the overall block propagation time.

Shuangjie Bai, Geng Yang, Chunming Rong, Guoxiu Liu · 5 authors

No abstract is available for this record.

Richard Banach

Summary The Bitcoin model originated blockchain architectures and inspired their further development. Blockchain architectures are still most commonly associated with currency applications, and with financial speculation. Bitcoin's rewards for Proof of Work mining became the default consensus technique for blockchains. As an alternative to reward mechanisms for blockchain maintenance, we propose punishment mechanisms for neglecting to maintain the blockchain (provided participants are intrinsically motivated to be beneficiaries of the blockchain application). Punishment not Reward is convincing for enterprise mission critical blockchain applications, and potential punishment mechanisms include denial of service and/or revocation of confidentiality . This obviates the need for reward via cryptocurrencies, along with their attendant volatility, insecure ecosystem, and market manipulation demerits. The privacy concerns of competing entities participating in a blockchain application are prima facie in conflict with the needs of the community to be able to inflict punishment mechanisms. Conflicts of this kind can be addressed via sophisticated cryptographic techniques such as secret sharing, multiparty computation, zero‐knowledge proofs, and so on, which play a vital role. We stress the importance of correctly balancing all application specific interests in the engineering of blockchain applications, so that the mix of incentives and disincentives is stabilizing.

Kejiao Li, Hui Li, Han Wang, Huiyao An · 7 authors

The blockchain has a great vogue in recent years, and its core consensus algorithms also become the focus of research. At present, most of the research on consensus mechanisms are oriented to the public blockchain and based on existing consensus mechanisms or sophisticated distributed algorithms. Various application scenarios have been developed based on the consortium blockchain, while few researchers pay attention to customize consistency algorithms. Moreover, there is a trade-off between security and performance in designing consensus mechanisms. We propose a novel consensus algorithm called Proof of Vote (PoV), where the distributed nodes controlled by consortium members could reach consensus and come to a decentralized arbitration by voting. PoV separates the voting rights and bookkeeping rights with the essential idea of establishing different security identities for network nodes. Contrary to the third-party intermediary or uncontrollable public awareness, the production and verification of PoV blocks are decided by the voting results among the core consortium members. We theoretically prove that PoV blocks can reach transaction finality by only one confirmation. Compared with the total traffic complexity of BFT-based consensus, PoV has just that of O( ), which is a great improvement when the number of nodes is over 100.

Hao Yin, Yihang Wei, Yuwen Li, Liehuang Zhu · 6 authors

No abstract is available for this record.

Hailin Chen, Gang Xu, Yuling Chen, Xiu‐Bo Chen · 8 authors

Most existing blockchain schemes are based on the design concept “openness and transparency” to realize data security, which usually require transaction data to be presented in the form of plaintext. However, it inevitably brings the issues with respect to data privacy and operating performance. In this paper, we proposed a novel blockchain scheme called Cipherchain, which can process and maintain transaction data in the form of ciphertext while the characteristics of immutability and auditability are guaranteed. Specifically in our scheme, transactions can be encrypted locally based on a searchable encryption scheme called multi-user public key encryption with conjunctive keyword search (mPECK), and can be accessed by multiple specific participants after appended to the globally consistent distributed ledger. By introducing execution-consensus-update paradigm of transaction flow, Cipherchain cannot only make it possible for transaction data to exist in the form of ciphertext, but also guarantee the overall system performance not greatly affected by cryptographic operations and other local execution work. In addition, Cipherchain is a promising scheme to realize the technology combination of “blockchain+cloud computing” and “permissioned blockchain+public blockchain”.

Gagandeep Kaur, Charu Gandhi

No abstract is available for this record.

Myoungwon Oh, Sujin Ha, Jin Hyuk Yoon, Kang‐Won Lee · 6 authors

Distributed ledger technology faces scalability problems due to a long commit time despite recent successes for cryptocurrency. Small group consensus studies have improved this scalability of distributed ledgers. However, they still have problems of the consensus process itself. For example, most blockchain systems perform serialized block proposal and consensus processing, guarantee the finality with high overhead, and handle byzantine nodes inefficiently. To address these problems, we propose a consensus system, named graph learning byzantine fault tolerance (GL BFT), which offers high parallelism and low latency under Byzantine fault. To do this, we enable a parallel pipelined agreement by separating the block proposal and the consensus process. Second, we devise two techniques of merging blocks and commit learning to guarantee the finality with little overhead. Finally, we present a path learning approach which chooses optimal paths to handle Byzantine fault. The proposed GL BFT can achieve instant finality with low message overhead among a small group of nodes even if Byzantine nodes exit. Also, we evaluate its performance on an open source blockchain protocol. Experimental results show that our design reduces data traffic required by the consensus up to 30%, one transaction is finalized within a few seconds, and optimal performance is maintained.

Trafim Lasy

The goal of this article is to extend the ideas concerning Bracha-Toueg asynchronous Byzantine Fault Tolerant consensus algorithm and Baird's Hashgraph consensus. We propose a family of atomic broadcast algorithms, which Hashgraph consensus is closely related to. We also do preliminary comparative algorithm speed analysis which shows that some members of the family seriously outperform Hashgraph consensus. These algorithms can also be readily used as a base of proof-of-stake consensuses. In appendix we provide an extension of Hashgraph gossip protocol, which efficiently handles byzantine fault information exchange between nodes.

Jie Niu, Xuelian Li, Juntao Gao, Yue Han

The Internet of Things (IoT) makes our life more intelligent. Its combination with the cloud server can solve big data processing problems to meet users' needs and bring us great convenience. However, there are two challenges we need to face: data sharing and key leakage. To solve the above challenges, attribute-based encryption (ABE) is used to achieve data sharing combined with searchable encryption (SE). Most of the existing attribute-based searchable encryption (SE) schemes are inefficient and not suitable for IoT devices because of the large amount of attributes and keys. The key-leakage problem is serious in practice which very little literature focused on it. In order to address both problems, in this article, we propose a key aggregation searchable encryption (KASE) scheme based on the blockchain with auxiliary input (AI), which is capable of achieving secure data sharing on the encrypted data. Our scheme is presented through a novel chosen plaintext attack (CPA) secure scheme. We prove our scheme is chosen ciphertext attack (CCA) secure against key leakage under the decisional Diffie-Hellman assumption and Goldreich-Leivin theorem. Moreover, we adopt the proposed scheme to establish a data-sharing system based on blockchain, which improves search efficiency and connects the global ecology. In addition, extensive performance evaluations are conducted, and the results indicate our scheme is really efficient in cloud-computing-enhanced IoT.

Jorge Peña Queralta, Tomi Westerlund

One of the key challenges in the collaboration within heterogeneous multi-robot systems is the optimization of the amount and type of data to be shared between robots with different sensing capabilities and computational resources. In this paper, we present a novel approach to managing collaboration terms in heterogeneous multi-robot systems with blockchain technology. Leveraging the extensive research of consensus algorithms in the blockchain domain, we exploit key technologies in this field to be integrated for consensus in robotic systems. We propose the utilization of proof of work systems to have an online estimation of the available computational resources at different robots. Furthermore, we define smart contracts that integrate information about the environment from different robots in order to evaluate and rank the quality and accuracy of each of the robots' sensor data. This means that the key parameters involved in heterogeneous robotic collaboration are integrated within the Blockchain and estimated at all robots equally without explicitly sharing information about the robots' hardware or sensors. Trustability is based on the verification of data samples that are submitted to the blockchain within each data exchange transaction and validated by other robots operating in the same environment. Initial results are reported which show the viability of the concepts presented in this paper.

Qiang Tang

Distributed Leger Technologies (DLTs), most notably Blockchain technologies, bring decentralised platforms that eliminate a single trusted third party and avoid the notorious single point of failure vulnerability. Since Nakamoto's Bitcoin cryptocurrency system, an enormous number of decentralised applications have been proposed on top of these technologies, aiming at more transparency and trustworthiness than their traditional counterparts. These applications spread over a lot of areas, e.g. financial services, healthcare, transportation, supply chain management, and cloud computing. While Blockchain brings transparency and decentralised trust intuitively due to the consensus of a (very large) group of nodes (or, miners), it introduces very subtle implications for other desirable properties such as privacy. In this work, we demonstrate these subtle implications for Blockchain-based searchable encryption solutions, which are one specific use case of cloud computing services. These solutions rely on Blockchain to achieve both the standard privacy property and the new fairness property, which requires that search operations are carried out faithfully and are rewarded accordingly. We show that directly replacing the server in an existing searchable encryption solution with a Blockchain will cause undesirable operational cost, privacy loss, and security vulnerabilities. The analysis results indicate that a dedicated server is still needed to achieve the desired privacy guarantee. To this end, we propose two frameworks which can be instantiated based on most existing searchable encryption schemes. Through analysing these two frameworks, we affirmatively show that a carefully engineered Blockchain-based solution can achieve the desired fairness property while preserving the privacy guarantee of the original searchable encryption scheme simultaneously.

Serdar Boztaş

The 3XORSUM problem aims to find (x, y, z) such that x + y + z = 0 over {0, 1}d, with each variable drawn from one of 3 randomly generated lists. In addition to being of interest in its own right, this problem has cryptographic applications including proof of stake methods in Blockchain.The 3XORSUM problem is also related to the integer 3SUM problem from theoretical computer science on which there is extensive recent literature. It is conjectured that the integer 3SUM problem has complexity $\tilde \Omega \left({{n^2}}\right)$ for lists of size O(n).Wagner [10] has presented an algorithm with complexity Õ(2d/3) for finding a 4XORSUM solution (x + y + z + w = 0) with each variable drawn from one of 4 randomly generated lists of size O(2d/3) with members from {0, 1}d.We present an algorithm which solves the 3XORSUM problem for randomly generated binary vectors from {0, 1}dwith time and memory complexity Õ(n) = Õ(2d/3). This substantially improves results from [1], [8]. Our algorithm has applications to blockchains and other cryptographic problems.

Rachid Guerraoui, Petr Kuznetsov, Matteo Monti, Matej Pavlovič · 5 authors

Many blockchain-based algorithms, such as Bitcoin, implement a decentralized asset transfer system, often referred to as a cryptocurrency. As stated in the original paper by Nakamoto, at the heart of these systems lies the problem of preventing double-spending; this is usually solved by achieving consensus on the order of transfers among the participants. In this paper, we treat the asset transfer problem as a concurrent object and determine its consensus number, showing that consensus is, in fact, not necessary to prevent double-spending. We first consider the problem as defined by Nakamoto, where only a single process---the account owner---can withdraw from each account. Safety and liveness need to be ensured for correct account owners, whereas misbehaving account owners might be unable to perform transfers. We show that the consensus number of an asset transfer object is $1$. We then consider a more general $k$-shared asset transfer object where up to $k$ processes can atomically withdraw from the same account, and show that this object has consensus number $k$. We establish our results in the context of shared memory with benign faults, allowing us to properly understand the level of difficulty of the asset transfer problem. We also translate these results in the message passing setting with Byzantine players, a model that is more relevant in practice. In this model, we describe an asynchronous Byzantine fault-tolerant asset transfer implementation that is both simpler and more efficient than state-of-the-art consensus-based solutions. Our results are applicable to both the permissioned (private) and permissionless (public) setting, as normally their differentiation is hidden by the abstractions on top of which our algorithms are based.

Peter Robinson

A Coordination Blockchain is a blockchain with the task of coordinating activities of multiple private blockchains. This paper discusses the pros and cons of using Ethereum MainNet, the public Ethereum blockchain, as a Coordination Blockchain. The requirements Ethereum MainNet needs to fulfil to perform this role are discussed within the context of Ethereum Private Sidechains, a private blockchain technology which allows many blockchains to be operated in parallel, and allows atomic crosschain transactions to execute across blockchains. Ethereum MainNet is a permissionless network which aims to offer strong authenticity, integrity, and non-repudiation properties, that incentivises good behaviour using crypto economics. This paper demonstrates that Ethereum MainNet does deliver these properties. It then provides a comprehensive review of the features of Ethereum Private Sidechains, with a focus on the potential usage of Coordination Blockchains for these features. Finally, the merits of using Ethereum MainNet as a Coordination Blockchain are assessed. For Ethereum Private Sidechains, we found that Ethereum MainNet is best suited to storing long term static data that needs to be widely available, such as the Ethereum Registration Authority information. However, due to Ethereum MainNet's probabilistic finality, it is not well suited to information that needs to be available and acted upon immediately, such as the Sidechain Public Keys and Atomic Crosschain Transaction state information that need to be accessible prior to the first atomic crosschain transaction being issued on a sidechain. Although this paper examined the use of Ethereum MainNet as a Coordination Blockchain within reference to Ethereum Private Sidechains, the discussions and observations of the typical tasks a Coordination blockchain may be expected to perform are applicable more widely to any multi-blockchain system.

Peter Robinson

A Coordination Blockchain is a blockchain with the task of coordinating\nactivities of multiple private blockchains. This paper discusses the pros and\ncons of using Ethereum MainNet, the public Ethereum blockchain, as a\nCoordination Blockchain. The requirements Ethereum MainNet needs to fulfil to\nperform this role are discussed within the context of Ethereum Private\nSidechains, a private blockchain technology which allows many blockchains to be\noperated in parallel, and allows atomic crosschain transactions to execute\nacross blockchains. Ethereum MainNet is a permissionless network which aims to\noffer strong authenticity, integrity, and non-repudiation properties, that\nincentivises good behaviour using crypto economics. This paper demonstrates\nthat Ethereum MainNet does deliver these properties. It then provides a\ncomprehensive review of the features of Ethereum Private Sidechains, with a\nfocus on the potential usage of Coordination Blockchains for these features.\nFinally, the merits of using Ethereum MainNet as a Coordination Blockchain are\nassessed. For Ethereum Private Sidechains, we found that Ethereum MainNet is\nbest suited to storing long term static data that needs to be widely available,\nsuch as the Ethereum Registration Authority information. However, due to\nEthereum MainNet's probabilistic finality, it is not well suited to information\nthat needs to be available and acted upon immediately, such as the Sidechain\nPublic Keys and Atomic Crosschain Transaction state information that need to be\naccessible prior to the first atomic crosschain transaction being issued on a\nsidechain. Although this paper examined the use of Ethereum MainNet as a\nCoordination Blockchain within reference to Ethereum Private Sidechains, the\ndiscussions and observations of the typical tasks a Coordination blockchain may\nbe expected to perform are applicable more widely to any multi-blockchain\nsystem.\n