Blockchain Papers

Gabriel Antonio F. Rebello, Gustavo F. Camilo, Lucas C. B. Guimarães, Lucas Airam C. de Souza · 6 authors

No abstract is available for this record.

Guichun Yuan, Liuping Feng, Jing Ning, Xiaoyu Yang

The PBFT (Practical Byzantine Fault Tolerant) is a consensus algorithm widely used in alliance blockchain, but there are some problems of high communication overhead and high latency. Therefore, the original PBFT consensus algorithm is improved in the paper. Firstly, the voting mechanism is introduced for the original PBFT algorithm. The nodes are divided into two classes: consensus node and ordinary node. The primary node is selected from the consensus nodes to lead the consensus process to ensure the reliability of the consensus results. Secondly, the consensus process of PBFT algorithm was optimized. The consensus process is simplified into three phases, which reduces the algorithm complexity and improves the consensus efficiency. The experiment shows that our improved PBFT algorithm has better performance than the original PBFT algorithm in communication overhead and consensus delay.

Nicholas Franzese, Jonathan Katz, Steve Lu, Rafail Ostrovsky · 6 authors

We show a constant-overhead interactive zero-knowledge (ZK) proof system for RAM programs, that is, a ZK proof in which the communication complexity as well as the running times of the prover and verifier scale linearly in the size of the memory N and the running time T of the underlying RAM program. Besides yielding an asymptotic improvement of prior work, our implementation gives concrete performance improvements for RAM-based ZK proofs. In particular, our implementation supports ZK proofs of private read/write accesses to 64~MB of memory (224 32-bit words) using only 34~bytes of communication per access, a more than 80x improvement compared to the recent BubbleRAM protocol. We also design a lightweight RISC CPU that can efficiently emulate the MIPS-I instruction set, and for which our ZK proof communicates only ~320 bytes per cycle, more than 10x less than the BubbleRAM CPU. In a 100 Mbps network, we can perform zero-knowledge executions of our CPU (with 64~MB of main memory and 4~MB of program memory) at a clock rate of 6.6 KHz.

Muhammad Saad, Afsah Anwar, Srivatsan Ravi, Aziz Mohaisen

The Bitcoin blockchain safety relies on strong network synchrony. Therefore, violating the blockchain safety requires strong adversaries that control a mining pool with ≈51% hash rate. In this paper, we show that the network synchrony does not hold in the real world Bitcoin network which can be exploited to feasibly violate the blockchain safety and chain quality. Towards that, first we construct the Bitcoin ideal functionality to formally specify its ideal execution model in a synchronous network. We then develop a large-scale data collection system through which we connect with more than 103K IP addresses of the Bitcoin nodes and identify 871 mining nodes. We contrast the ideal functionality against the real world measurements to expose the network anomalies that can be exploited to optimize the existing attacks. Particularly, we observe a non-uniform block propagation pattern among the mining nodes showing that the Bitcoin network is asynchronous in practice. To realize the threat of an asynchronous network, we present the HashSplit attack that allows an adversary to orchestrate concurrent mining on multiple branches of the blockchain to violate common prefix and chain quality properties. We also propose the attack countermeasures by tweaking Bitcoin Core to model the Bitcoin ideal functionality. Our measurements, theoretical modeling, proposed attack, and countermeasures open new directions in the security evaluation of Bitcoin and similar blockchain systems.

Muhammad Saad, Songqing Chen, Aziz Mohaisen

The existing Bitcoin security research has mainly followed the security models in [22, 35], which stipulate that an adversary controls some mining power in order to violate the blockchain consistency property (i.e., through a double-spend attack). These models, however, largely overlooked the impact of the realistic network synchronization, which can be manipulated given the permissionless nature of the network. In this paper, we revisit the security of Bitcoin blockchain by incorporating the network synchronization into the security model and evaluating that in practice. Towards this goal, we propose the ideal functionality for the Bitcoin network synchronization and specify bounds on the network outdegree and the block propagation delay in order to preserve the consistency property. By contrasting the ideal functionality against measurements, we find deteriorating network synchronization reported by Bitnodes and a notable churn rate with 10% of the nodes arriving and departing from the network daily.

Luc Gerrits, Cyril Naves Samuel, Roland Kromes, François Verdier · 6 authors

Private or consortium blockchain networks have fewer verified participants and offer better throughput and transaction efficiency than public networks. However, as more and more blockchain consensuses are designed for private or consortium networks, their performances are often estimated without a practical use case implementation. In our use case, participants do not have to trust each other but still work together to build an ecosystem where users control their data and information. This paper analyzes the performance (transaction throughput, rejections, node participants) of Byzantine Fault Tolerant Consensus (BFT) using two blockchains: Hyperledger Sawtooth and Ethereum.

Mounzer Saijare, İ̇hsan Tolga Medeni, Tunç D. Medeni, Mehmet Serdar Güzel

Ethereum databases with their huge security and integrity can provide perfect mechanism for storing and sharing the data of the highly important projects. Qualitative and quantitative research methods were used in this paper to design software for Ethereum databases. Also, these methods were used to examine how and how much features can be added to the software. Designing the software considered the barriers and the limitations of Solidity smart contracts programming language and Ethereum blockchain platform. The achieved software can make any Ethereum database with parent-child relationships in between the tables. More professional features will be added in future research as soon as possible. The study used survey method to discuss recommended applications for the software integration with another software for ESRI digital maps programming. The recommended applications are the real estate business full automation and the transparent environmental management to protect the Mediterranean Sea from the pollution. However, most parts related to Ethereum databases software are covered. But to keep this paper in reasonable size, only the survey is included for the parts related to the software recommended applications with the digital maps software.

Jintian Fu, Lupeng Zhang, Leixin Wang, Fengqi Li

With the vigorous development of 5G communication technology, massive Internet of Things (IoT) devices generate data incrementally. Different data owners control different private domains of the IoT through edge devices and hope to achieve credible data sharing. Most of the existing solutions are based on blockchain to realize cross-domain IoT data sharing. However, incremental IoT data sharing has dual requirements for the consensus mechanism to be efficient and Byzantine fault tolerant. The independent use of the existing consensus mechanism cannot meet the above requirements simultaneously. Therefore, we propose an efficient and fault-tolerant blockchain consensus transform (BCT) mechanism for IoT. In addition, we design two consensus algorithms, namely, detectable RAFT (DRAFT) and double-layer parallel BFT (DPBFT), to improve the efficiency and fault tolerance of the data-sharing process. Extensive experiments have been conducted to show the efficiency and tolerance of our BCT mechanism.

Liuyang Ren, Paul A. S. Ward

While many researchers adopt a sharding approach to design scaling blockchains, few works have studied the transaction placement problem incurred by sharding protocols. The widely-used hashing placement algorithm renders an overwhelming portion of transactions as cross-shard. In this paper, we analyze the high cost of cross-shard transactions and reveal that most Bitcoin transactions have simple dependencies and can become single-shard under a placement algorithm taking transaction dependencies into account. In addition, we perform a case study of OptChain, which is the state-of-the-art transaction placement algorithm for sharded blockchains, and find a shortcoming of it. A fix is proposed, and our evaluation results demonstrate that the fix helps OptChain improve the system throughput by 4x.

Parth Thakkar, Senthilnathan Natarajan

Large cloud providers such as AWS and IBM now provide managed blockchain platforms, showcasing an active interest in blockchains. Unfortunately, blockchains provide poor performance and scalability. This is true even for the Execute-Order-Validate (EOV) style of blockchains which improves over the traditional Order-Execute architecture. We experimentally show that EOV platforms scale poorly using both vertical and horizontal scaling approaches. We find that the throughput is bottlenecked by the Validation and Commit phases, which poorly utilize the resources, limiting performance and scalability.

Denis Avrilionis, Thomas Hardjono

Today there is considerable interest in deploying blockchains and\ndecentralized ledger technology as a means to address the deficiencies of\ncurrent financial and digital asset infrastructures. The focal point of\nattention in many projects on digital asset and cryptocurrency is centered\naround blockchain systems and smart contracts. Many projects seek to make the\nblockchain as the centerpiece of the new decentralized world of finance.\nHowever, several roadblocks and challenges currently face this predominant\nblockchain-centric view. In this paper we argue that the proper and correct\nperspective on decentralized economy should be one that is asset-centric, where\nthe goal should be the consistent lifecycle management of assets in the\nreal-world with their digital representation on the blockchain. We introduce\nthe notion of the digital twin to capture the relationship between a real-world\nasset and its on-chain representation. A digital twin container is utilized to\npermit off-chain state persistence and on-chain state traceability, where the\ncontainer can be deployed on the blockchain as well as on traditional\napplication servers. The digital twin container becomes the bridge between\nlegacy infrastructures and the newly emergent blockchain infrastructures,\npermitting legacy systems to interoperate consistently with blockchain systems.\nWe believe this asset-centric view to be the correct evolutionary direction for\nthe nascent field of blockchains and decentralized ledger technology.\n

Guntur Dharma Putra, Volkan Dedeoglu, Abhinav Pathak, Salil S. Kanhere · 5 authors

Intrusion Detection Systems (IDS) have been the industry standard for securing IoT networks against known attacks. To increase the capability of an IDS, researchers proposed the concept of blockchain-based Collaborative-IDS (CIDS), wherein blockchain acts as a decentralised platform allowing collaboration between CIDS nodes to share intrusion related information, such as intrusion alarms and detection rules. However, proposals in blockchain-based CIDS overlook the importance of continuous evaluation of the trustworthiness of each node and generally work based on the assumption that the nodes are always honest. In this paper, we propose a decentralised CIDS that emphasises the importance of building trust between CIDS nodes. In our proposed solution, each CIDS node exchanges detection rules to help other nodes detect new types of intrusion. Our architecture offloads the trust computation to the blockchain and utilises a decentralised storage to host the shared trustworthy detection rules, ensuring scalability. Our implementation in a lab-scale testbed shows that the our solution is feasible and performs within the expected benchmarks of the Ethereum platform.

Chen Yang, Zhongxin Guo, Runhuai Li, Shuo Chen · 7 authors

Ethereum is an emerging distributed computing platform that supports a decentralized replicated virtual machine at a large scale. Transactions in Ethereum are specified in smart contracts, disseminated through broadcast, accepted into the chain of blocks, and then executed on each node. In this new Dissemination-Consensus-Execution (DiCE) paradigm, the time interval between when a transaction is known (during the dissemination phase) to when the transaction is executed (after the consensus phase) offers a window of opportunity to accelerate transaction processing through speculative execution. However, the traditional speculative execution, which hinges on the ability to predict the future accurately, is inadequate because of DiCE's many-future nature.

Caspar Schwarz-Schilling, Joachim Neu, Barnabé Monnot, Aditya Asgaonkar · 6 authors

Recently, two attacks were presented against Proof-of-Stake (PoS) Ethereum: one where short-range reorganizations of the underlying consensus chain are used to increase individual validators' profits and delay consensus decisions, and one where adversarial network delay is leveraged to stall consensus decisions indefinitely. We provide refined variants of these attacks, considerably relaxing the requirements on adversarial stake and network timing, and thus rendering the attacks more severe. Combining techniques from both refined attacks, we obtain a third attack which allows an adversary with vanishingly small fraction of stake and no control over network message propagation (assuming instead probabilistic message propagation) to cause even long-range consensus chain reorganizations. Honest-but-rational or ideologically motivated validators could use this attack to increase their profits or stall the protocol, threatening incentive alignment and security of PoS Ethereum. The attack can also lead to destabilization of consensus from congestion in vote processing.

Diego Romano, Giovanni Schmid

In the last four years, the evolution and adoption of blockchain and, more generally, distributed ledger systems have shown the affirmation of many concepts and models with significant differences in system governance and suitable applications. This work aims to analyze distributed ledger technology (DLT) critically. Starting from the topical idea of decentralization, we introduce concepts and building blocks currently adopted in the available systems centering on their functional aspects and impact on possible applications. We present some conceptual framing tools helpful in the application context: a DLT reference architecture, off-chain and on-chain governance models, and classification of consensus protocols. Finally, we introduce the concept of process authenticity, reviewing tools and strategies for integrating DLT with the physical world and proposing a constructive scheme for the authentication of a physical resource through alphanumeric data.

Nouraldin Jaber, Christopher Wagner, Swen Jacobs, Milind Kulkarni · 5 authors

The last decade has sparked several valiant efforts in deductive verification of distributed agreement protocols such as consensus and leader election. Oddly, there have been far fewer verification efforts that go beyond the core protocols and target applications that are built on top of agreement protocols. This is unfortunate, as agreement-based distributed services such as data stores, locks, and ledgers are ubiquitous and potentially permit modular, scalable verification approaches that mimic their modular design. We address this need for verification of distributed agreement-based systems through our novel modeling and verification framework, QuickSilver, that is not only modular, but also fully automated. The key enabling feature of QuickSilver is our encoding of abstractions of verified agreement protocols that facilitates modular, decidable, and scalable automated verification. We demonstrate the potential of QuickSilver by modeling and efficiently verifying a series of tricky case studies, adapted from real-world applications, such as a data store, a lock service, a surveillance system, a pathfinding algorithm for mobile robots, and more.

M. L. Horton, Xiaohua Wen, Yudan Yi

RTK technology is now expanding from the traditional geo-spatial communities (such as, surveying applications, construction machine and precision farming) to automotive markets, and is becoming the key and essential component for autonomous driving. Traditionally, RTK corrections, normally in RTCM standard format, are generated from a centralized server using a complicated GNSS algorithm (for example, VRS (Virtual Reference Station) or MAC (Master Auxiliary Correction)) and the raw GNSS measurements from a set of GNSS reference stations (normally in the order of tens to hundreds). Due to the computational and network connection limitations, such systems (for example, Trimble’s VRSNet, Leica’s SpiderNET and Topcon’s TopNET) to provide RTK services, can only handle hundreds’ GNSS reference stations and thousands of user connections for RTK corrections. Also due to the complexity of algorithms to generate the corrections and operating a GNSS network, nowadays, RTK correction services are only locked by government institutions and large private companies. Or you need to setup a base station by yourself, which requires a lot of professional experience, thus it doesn't scale, and not applicable sometimes. The rapid development of autonomous driving market requires a large scale (national-wide or global) RTK network correction service, for example, Qianxun SI is spending huge efforts to build a nationalwide RTK correction service in China, especially design for autonomous driving market in China. This paper describe a new network model---PAS(Precision as Service). PAS employs a blockchain secured by a Proof-of-Stake and Proof-of-Accuracy (POA) hybrid as the consensus model. Proof-of-Stake(POS) is a consensus protocol widely used in recent blockchain projects. In our setup, service provider miners (validator, v-node) need to stake tokens to participate in system consensus. Each node will have its chance to produce blocks based on the BLS algorithm weighted by the staked token. We use the BLS algorithm for fast and reliable BFT-like (Byzantine Fault Tolerant) consensus. Multiple parties use threshold signature to reach an agreement on a blockchain proposal. The staking will also improve economic security by punishing any misbehaving validators. Anyone who owns a PAS token can bond (or delegate) their coins and become a validator, making the validator set open and permissionless. Similar to POW, POA requires external resource consumption to add entropy to the system. This external resource is in the form of physical geospatial coordinates. It is unique, computationally inexpensive, yet fully decentralized available to a large group of people. With very affordable RTK hardware, each base station miner can provide accurate RTK location streaming data with their unique geospatial coordinates. Service provider miners collect those streaming data, verifying the data's accuracy relative to their physical position, creating proof of accurate geographic span in a cryptographically secure way. POS and POA's combination is to create a fast, scalable, and secure blockchain for various applications on top of it. BLS signature By using a curve pair, BLS signature can be used to verify that the point pairs on the two (or the same) curves conform to the multiplicative commutative law: e(P, Q) ? n e(x×P, Q) = e(P, x×Q). The threshold signature (threshold sig) is essentially the signature method of m-of-n. Under the condition that m signatures are known, a unique and valid signature can be synthesized. The combination of any m signature fragments is the same verifiable signature. If fewer than m fragments are shared on the network, no individual will know the full signature. So even with many parties, the BLS signature size could be as small as the size of one signature. That will improve the efficiency of data storage of blockchain-based systems. Also, the BLS signature could be viewed as a robust random seed, as any party can not guess the combined signature, yet it can be verified quickly by everyone. Token economics Token will play an essential role inside the PAS platform. The native token in the PAS platform is called PCS. PCS's primary functions are in staking, payment method for all applications or services in the PAS platform. PCS tokens will also be used to pay transaction fees and the reward for miners and validators. Reward Types Reward Users of PCS stake tokens to subsidize operating and capital expenditures. A reward can happen in two ways. A. Stakers can stake tokens to active Service Provider Miner. Each staked token will be rewarded proportionally according to the set inflation ratio. B. Base Station Miner can uniquely bind to a Service Provider Miner. Once bound, Base Station Miner will stream accuracy RTK data to Service Provider Miner. Service Provider Miner will validate the data and use the combined geospatial RTK coverage map inside the block proposal for additional token reward, besides the staked token reward. In return, Service Provider Miner will distribute mining rewards back to Base Station Miners. Additionally, Service Provider can provide accurate location service to end customer such as surveyor, autonomous vehicle, drone, etc. Service Providers can market their service to an intended user group and create a service payment plan. Service Provider's revenue can be split among Base Station Miner in a preset distribution contract, in the form of a smart contract in PAS Network, or even an off-chain contract. Limits on Number of Validators At the PAS Network's initial stage, the number of validators will be limited to a certain number (e.g., 64). The number of validators will increase gradually as the PAS Network coverage increases. The selection of validators will be based on the balanced consideration of staked token and RTK map coverage area associated with that validator. Staked token RTK data stream Services Provider Staking reward Data reward Base station miner Staker Reward System A Service Provider Miner commits to provide services for at least time t and intends to earn service income r based on staked token T. The minimal number of Base Station Miners is about 10,000. To ensure robust service with enough system redundancy, the ideal number of base station miners could be 3x. Base Station Miners' density may vary from area to area, as the demand for RTK service may change dramatically.

Reiji Kobayashi, Atsushi Kanai

Quiz sites are typically made up of a front end, a back end, and a database of questions. Our objective is to further commonize this structure. Problem verification and solution keeping are aspects that have already been thoroughly studied and modified. However, the fairness of answer validation is often unclear to the end user. We propose a system that reduces the cost of creating a quiz site and a quiz scoring system for e-learning by putting part of the structure on a blockchain. Our system verifies answers using zero-knowledge proofs, stores the answers with Ethereum, an open-source platform for decentralized applications, and tracks them. Blockchain can be used to prevent the falsification of answer records. Ethereum is a new technique that has attracted considerable attention in recent years, and we use its program executions, i.e., smart contracts, to validate answers. After receiving an answer, the system stores it as an Ethereum transaction event.

Johannes Sedlmeir, Tim Wagner, Emil Djerekarov, Ryan Green · 6 authors

Enterprises have been attracted by the capability of blockchains to provide a single source of truth for workloads that span companies, geographies, and clouds while retaining the independence of each party's IT operations. However, so far production applications have remained rare, stymied by technical limitations of existing blockchain technologies and challenges with their integration into enterprises' IT systems. In this paper, we collect enterprises' requirements on distributed ledgers for data sharing and integration from a technical perspective, argue that they are not sufficiently addressed by available blockchain frameworks, and propose a novel distributed ledger design that is "serverless", i.e., built on cloud-native resources. We evaluate its qualitative and quantitative properties and give evidence that enterprises already heavily reliant on cloud service providers would consider such an approach acceptable, particularly if it offers ease of deployment, low transactional cost structure, and a combination of latency and scalability aligned with real-time IT application needs.

Qian Hu, Weibin Chen, Yang‐Yang Chen

No abstract is available for this record.

Paolo Bottoni, Anna Labella, Remo Pareschi

A key component of blockchain technology is the ledger, viz., a database that, unlike standard databases, keeps in memory the complete history of past transactions as in a notarial archive for the benefit of any future test. In second-generation blockchains such as Ethereum the ledger is coupled with smart contracts, which enable the automation of transactions associated with agreements between the parties of a financial or commercial nature. The coupling of smart contracts and ledgers provides the technological background for very innovative application areas, such as Decentralized Autonomous Organizations (DAOs), Initial Coin Offerings (ICOs) and Decentralized Finance (DeFi), which propelled blockchains beyond cryptocurrencies that were the only focus of first generation blockchains such as the Bitcoin. However, the currently used implementation of smart contracts as arbitrary programming constructs has made them susceptible to dangerous bugs that can be exploited maliciously and has moved their semantics away from that of legal contracts. We propose here to recompose the split and recover the reliability of databases by formalizing a notion of contract modelled as a finite-state automaton with well-defined computational characteristics derived from an encoding in terms of allocations of resources to actors, as an alternative to the approach based on programming. To complete the work, we use temporal logic as the basis for an abstract query language that is effectively suited to the historical nature of the information kept in the ledger.

Nur Arifin Akbar, Andi Sunyoto, M. Rudyanto Arief, Wahyu Caesarendra

Today, there is a tendency to reduce the dependence on local computation in favor of cloud computing. However, this inadvertently increases the reliance upon distributed fault-tolerant systems. In a condition that forced to work together, these systems often need to reach an agreement on some state or task, and possibly even in the presence of some misbehaving Byzantine nodes. Although non-trivial, Byzantine Agreement (BA) protocols now exist that are resilient to these types of faults. However, there is still a risk for inconsistencies in the application state in practice, even if a BA protocol is used. A single transient fault may put a node into an illegal state, creating a need for new self-stabilizing BA protocols to recover from illegal states. As self-stabilization often comes with a cost, primarily in the form of communication overhead, a potential lowering of latency - the cost of each message - could significantly impact how fast the protocol behaves overall. Thereby, there is a need for new network protocols such as QUIC, which, among other things, aims to reduce latency. In this paper, we survey current state-of-the-art agreement protocols. Based on previous work, some researchers try to implement pseudocode like QUIC protocol for Ethereum blockchain to have a secure network, resulting in slightly slower performance than the IP-based blockchain. We focus on consensus in the context of blockchain as it has prompted the development and usage of new open-source BA solutions that are related to proof of stake. We also discuss extensions to some of these protocols, specifically the possibility of achieving self-stabilization and the potential integration of the QUIC protocol, such as PoS and PBFT. Finally, further challenges faced in the field and how they might be overcome are discussed.

Sebastian Friebe, Oliver Stengele, Hannes Hartenstein, Martina Zitterbart

When software systems become more complex, it can be advantageous to partition their code into multiple, separate components. In this work, we examine how multiple smart contracts can be coupled to work together. When coupling smart contracts, different design approaches are possible with their own advantages and disadvantages. As an example, we couple two smart contract applications on the Ethereum blockchain: Palinodia and DecentID. Palinodia can be used to ensure the integrity of downloaded executable binaries by checking their hashes against the hashes stored in the blockchain. To make sure that not everyone can modify the data stored on the blockchain, an identity management system is required. This task is fulfilled by DecentID, which provides decentralized identities stored as smart contracts on the blockchain. We evaluate approaches of coupling these two applications and discuss their benefits and drawbacks for this use case.

Babu Pillai, Kamanashis Biswas, Zhé Hóu, Vallipuram Muthukkumarasamy

No abstract is available for this record.