2023/02 のarXiv ブロックチェーン関連新着論文概要 DeepL翻訳





Published at 2023/02/08 13:42:48 (JST)

Blockchain-based certificate authentication system with enabling correction


Blockchain has proven to be an emerging technology in the digital world, changing the way everyone thinks about data security and bringing efficiency to several industries. It has already been applied to a wide range of applications, from financial services and supply chain management to voting systems and identity verification. An organization must verify its candidates before selecting them. Choosing an unqualified candidate can ruin an organization's reputation. In this digital era, many key fraudulent schemes are rampant in many companies and one of them is certificate fraud. It is possible to validate a candidate's qualifications using traditional methods, but there are drawbacks such as security issues and time consumption. In this paper, a blockchain-based academic certificate authentication system will be used to ensure authenticity and make the assertion of the decentralized system secure. However, the system will generate, authenticate and make corrections on academic certificates. Ultimately, some blockchain-based authentication systems already exist, they can't correct any errors that occur during generation. The proposed system will help in many ways, such as providing a user-friendly university admission, and smooth job hiring process, etc. In conclusion, our proposed system can permanently eradicate certificate forgeries and create and promote trust in society.


Published at 2023/02/10 01:25:31 (JST)

Improving Blockchain Scalability with the Setchain Data-type


Blockchain technologies are facing a scalability challenge, which must be overcome to guarantee a wider adoption of the technology. This scalability issue is due to the use of consensus algorithms to guarantee the total order of the chain of blocks and of the transactions within each block. However, total order is often not fully necessary, since important advanced applications of smart-contracts do not require a total order among all operations. A much higher scalability can potentially be achieved if a more relaxed order can be exploited. In this paper, we propose a novel distributed concurrent data type, called Setchain, which improves scalability significantly. A Setchain implements a grow-only set whose elements are not ordered, unlike conventional blockchain operations. When convenient, the Setchain allows forcing a synchronization barrier that assigns permanently an epoch number to a subset of the latest elements added, agreed by consensus. Therefore, two operations in the same epoch are not ordered, while two operations in different epochs are ordered by their respective epoch number. We present different Byzantine-tolerant implementations of Setchain, prove their correctness and report on an empirical evaluation of a prototype implementation. Our results show that Setchain is orders of magnitude faster than consensus-based ledgers, since it implements grow-only sets with epoch synchronization instead of total order. Since Setchain barriers can be synchronized with the underlying blockchain, Setchain objects can be used as a sidechain to implement many decentralized solutions with much faster operations than direct implementations on top of blockchains. Finally, we also present an algorithm that encompasses in a single process the combined behavior of Byzantine servers, which simplifies correctness proofs by encoding the general attacker in a concrete implementation.


Published at 2023/02/10 04:33:04 (JST)

Fee-Redistribution Smart Contracts for Transaction-Fee-Based Regime of Blockchains with the Longest Chain Rule

本論文では、最長チェーンフォーク選択ルールを持つプルーフ・オブ・ワーク(PoW)型ブロックチェーンの取引手数料ベースの体制におけるアンダーカット攻撃についてレビューしている。次に、マイニング収益の変動とマイニングギャップの問題、すなわち、取引手数料からの即時報酬が採掘者の支出をカバーできない状況に注目する。 これらの問題を軽減するために、我々は、採掘されたブロックからの取引手数料を2つに分割するソリューションを提案する。(1)ブロックの採掘者への即時報酬と、(2)合意プロトコルの一部である一つ以上の手数料再配分スマートコントラクト($mathcal{FRSC}$s)に送られる保証金である。同時に、これらの再分配スマートコントラクトは、ブロックのマイナーに、あらかじめ定義された時間の間、入ってくる手数料の累積資金の一定の割合を報酬として与えます。この設定により、プロトコルのインセンティブ安定性とセキュリティに有益ないくつかの興味深い特性を達成することができます。 我々の解決策により、アンダーカット攻撃を厳密に実行しないDefault-Compliantマイナーの割合は、最新技術の結果である66%から30%に低下しました。

In this paper, we review the undercutting attacks in the transaction-fee-based regime of proof-of-work (PoW) blockchains with the longest chain fork-choice rule. Next, we focus on the problem of fluctuations in mining revenue and the mining gap - i.e., a situation, in which the immediate reward from transaction fees does not cover miners' expenditures. To mitigate these issues, we propose a solution that splits transaction fees from a mined block into two parts - (1) an instant reward for the miner of a block and (2) a deposit sent to one or more fee-redistribution smart contracts ($\mathcal{FRSC}$s) that are part of the consensus protocol. At the same time, these redistribution smart contracts reward the miner of a block with a certain fraction of the accumulated funds of the incoming fees over a predefined time. This setting enables us to achieve several interesting properties that are beneficial for the incentive stability and security of the protocol. With our solution, the fraction of Default-Compliant miners who strictly do not execute undercutting attacks is lowered from the state-of-the-art result of 66% to 30%.


Published at 2023/02/13 17:38:01 (JST)

A Reference Architecture for Blockchain-based Traceability Systems Using Domain-Driven Design and Microservices


Traceability systems are important for solving problems due to the increasing scale of the global supply chain, such as food safety crises and market disorder. Blockchain, as an immutable and decentralized ledger, is able to optimize the traditional traceability system by ensuring the transparency and reliability of the system data. However, the use of blockchain technology may lead to a rapid increase in the complexity of system design and development. It is challenging to address widespread and complicated business, changeable processes, and massive data in practice, which are the main factors restricting the wide application of a blockchain-based traceability system (BTS). Therefore, in this paper, we reviewed relevant studies and proposed a reference architecture for BTSs. The proposed reference architecture can improve the cohesiveness, maintainability, and extensibility of BTSs through domain-driven design (DDD) and microservices. Considering the efficiency reduction caused by massive data and complicated data structure, we further changed the traditional single blockchain framework into multiple sub-chain networks, which could improve development efficiency and system performance. With the guidance of the architecture trade-off analysis method (ATAM), we evaluated our reference architecture and implemented a prototype in the salmon supply chain scenario. The results show that our solution is effective and adaptable to meet the requirements of BTSs.


Published at 2023/02/13 15:53:54 (JST)

PRAGTHOS:Practical Game Theoretically Secure Proof-of-Work Blockchain

ブロックチェーン技術の安全性解析は、活発な研究領域である。Proof-of-Work (PoW) ブロックチェーンについては、暗号的な安全性解析とゲーム理論的な安全性解析の両方が行われています。代表的な研究としては、Universal Composableフレームワークによる暗号的安全性解析と、Rational Protocol Designを用いたゲーム理論的安全性解析があります。これらの安全性解析モデルは、成立しない可能性のあるより厳格な仮定に依存している。本論文では、PoWブロックチェーンプロトコルの安全性を分析する。まず、これまでのモデルによる仮定が現実には有効でない場合があることを示し、攻撃者がこれらのモデルが捉えられない攻撃を仕掛けるために悪用することができることを示します。このような攻撃には、0.5未満の採掘力を持つ敵対者でもフォークが可能なDifficulty Alternating Attack、利己的採掘攻撃の一般的な境界であるQuick-Fork Attack、取引保留攻撃などが含まれます。続いて、従来の安全性解析モデルがこれらの攻撃を捕捉できない理由を論証し、より実用的な安全性解析の枠組みであるpRPDを提案します。次に、上記の攻撃から安全なPoWブロックチェーンPRAGTHOSを構築するためのフレームワークを提案する。最後に、PRAGTHOSフレームワークに準拠したPoWブロックチェーンは、報酬スキームに関する特定の条件下で、計算量的に拘束された敵対者に対して安全であることを論証する。

Security analysis of blockchain technology is an active domain of research. There has been both cryptographic and game-theoretic security analysis of Proof-of-Work (PoW) blockchains. Prominent work includes the cryptographic security analysis under the Universal Composable framework and Game-theoretic security analysis using Rational Protocol Design. These security analysis models rely on stricter assumptions that might not hold. In this paper, we analyze the security of PoW blockchain protocols. We first show how assumptions made by previous models need not be valid in reality, which attackers can exploit to launch attacks that these models fail to capture. These include Difficulty Alternating Attack, under which forking is possible for an adversary with less than 0.5 mining power, Quick-Fork Attack, a general bound on selfish mining attack and transaction withholding attack. Following this, we argue why previous models for security analysis fail to capture these attacks and propose a more practical framework for security analysis pRPD. We then propose a framework to build PoW blockchains PRAGTHOS, which is secure from the attacks mentioned above. Finally, we argue that PoW blockchains complying with the PRAGTHOS framework are secure against a computationally bounded adversary under certain conditions on the reward scheme.


Published at 2023/02/14 19:42:17 (JST)

Dissecting Bitcoin and Ethereum Transactions: On the Lack of Transaction Contention and Prioritization Transparency in Blockchains


In permissionless blockchains, transaction issuers include a fee to incentivize miners to include their transaction. To accurately estimate this prioritization fee for a transaction, transaction issuers (or blockchain participants, more generally) rely on two fundamental notions of transparency, namely contention and prioritization transparency. Contention transparency implies that participants are aware of every pending transaction that will contend with a given transaction for inclusion. Prioritization transparency states that the participants are aware of the transaction or prioritization fees paid by every such contending transaction. Neither of these notions of transparency holds well today. Private relay networks, for instance, allow users to send transactions privately to miners. Besides, users can offer fees to miners via either direct transfers to miners' wallets or off-chain payments -- neither of which are public. In this work, we characterize the lack of contention and prioritization transparency in Bitcoin and Ethereum resulting from such practices. We show that private relay networks are widely used and private transactions are quite prevalent. We show that the lack of transparency facilitates miners to collude and overcharge users who may use these private relay networks despite them offering little to no guarantees on transaction prioritization. The lack of these transparencies in blockchains has crucial implications for transaction issuers as well as the stability of blockchains. Finally, we make our data sets and scripts publicly available.


Published at 2023/02/14 06:44:38 (JST)

DeFi and NFTs Hinder Blockchain Scalability


Many classical blockchains are known to have an embarrassingly low transaction throughput, down to Bitcoin's notorious seven transactions per second limit.Various proposals and implementations for increasing throughput emerged in the first decade of blockchain research. But how much concurrency is possible? In their early days, blockchains were mostly used for simple transfers from user to user. More recently, however, decentralized finance (DeFi) and NFT marketplaces have completely changed what is happening on blockchains. Both are built using smart contracts and have gained significant popularity. Transactions on DeFi and NFT marketplaces often interact with the same smart contracts. We believe this development has transformed blockchain usage. In our work, we perform a historical analysis of Ethereum's transaction graph. We study how much interaction between transactions there was historically and how much there is now. We find that the rise of DeFi and NFT marketplaces has led to an increase in "centralization" in the transaction graph. More transactions are now interconnected: currently there are around 200 transactions per block with 4000 interdependencies between them. We further find that the parallelizability of Ethereum's current interconnected transaction workload is limited. A speedup exceeding a factor of five is currently unrealistic.


Published at 2023/02/20 23:35:38 (JST)

Defending against the nothing-at-stake problem in multi-threaded blockchains


In blockchain systems, the scarcity of a resource is used as a Sybil protection mechanism. In Proof-of-Work blockchains, that resource is computing power. In the event of a fork, the scarcity of this resource theoretically prevents miners from producing blocks on both branches of a fork. In Proof-of-Stake blockchains, because that resource is token stake, the computational cost of creating a block is negligible. In the event of a fork, and if no specific measures have been taken, rational block producers should extend both branches of the fork. In blockchains with sequential block production, a punishment mechanism known as slashing is often cited as a protection against the nothing-at-stake problem. However, in the context of a blockchain with parallel block production, it seems that slashing is not sufficient against the numerous divergence opportunities. In this paper, we propose a novel protection against the nothing-at-stake problem that takes the most out of BFT and Nakamoto-based consensus. By combining those approaches, we wish to scale up blockchains by allowing parallel block production without reconciliation.


Published at 2023/02/22 03:58:32 (JST)

Combining Blockchain and Biometrics: A Survey on Technical Aspects and a First Legal Analysis


Biometric recognition as a unique, hard-to-forge, and efficient way of identification and verification has become an indispensable part of the current digital world. The fast evolution of this technology has been a strong incentive for integrating it into many applications. Meanwhile, blockchain, the very attractive decentralized ledger technology, has been widely received both by the research and industry in the past years and it is being increasingly deployed nowadays in many different applications, such as money transfer, IoT, healthcare, or logistics. Recently, researchers have started to speculate what would be the pros and cons and what would be the best applications when these two technologies cross paths. This paper provides a survey of technical literature research on the combination of blockchain and biometrics and includes a first legal analysis of this integration to shed light on challenges and potentials. While this combination is still in its infancy and a growing body of literature discusses specific blockchain applications and solutions in an advanced technological set-up, this paper presents a holistic understanding of blockchains applicability in the biometric sector. This study demonstrates that combining blockchain and biometrics would be beneficial for novel applications in biometrics such as the PKI mechanism, distributed trusted service, and identity management. However, blockchain networks at their current stage are not efficient and economical for real-time applications. From a legal point of view, the allocation of accountability remains a main issue, while other difficulties remain, such as conducting a proper Data Protection Impact Assessment. Finally, it supplies technical and legal recommendations to reap the benefits and mitigate the risks of the combination.


Published at 2023/02/21 17:44:45 (JST)

Energy-Efficient Blockchain-enabled User-Centric Mobile Edge Computing


In the traditional mobile edge computing (MEC) system, the availability of MEC services is greatly limited for the edge users of the cell due to serious signal attenuation and inter-cell interference. User-centric MEC (UC-MEC) can be seen as a promising solution to address this issue. In UC-MEC, each user is served by a dedicated access point (AP) cluster enabled with MEC capability instead of a single MEC server, however, at the expense of more energy consumption and greater privacy risks. To achieve efficient and reliable resource utilization with user-centric services, we propose an energy efficient blockchain-enabled UC-MEC system where blockchain operations and resource optimization are jointly performed. Firstly, we design a resource-aware, reliable, replicated, redundant, and fault-tolerant (R-RAFT) consensus mechanism to implement secure and reliable resource trading. Then, an optimization framework based on alternating direction method of multipliers (ADMM) is proposed to minimize the total energy consumed by wireless transmission, consensus and task computing, where APs clustering, computing resource allocation and bandwidth allocation are jointly considered. Simulation results show superiority of the proposed UC-MEC system over reference schemes, at most 33.96% reduction in the total delay and 48.77% reduction in the total energy consumption.


Published at 2023/02/28 03:43:11 (JST)

Proof-of-Contribution-Based Design for Collaborative Machine Learning on Blockchain


We consider a project (model) owner that would like to train a model by utilizing the local private data and compute power of interested data owners, i.e., trainers. Our goal is to design a data marketplace for such decentralized collaborative/federated learning applications that simultaneously provides i) proof-of-contribution based reward allocation so that the trainers are compensated based on their contributions to the trained model; ii) privacy-preserving decentralized model training by avoiding any data movement from data owners; iii) robustness against malicious parties (e.g., trainers aiming to poison the model); iv) verifiability in the sense that the integrity, i.e., correctness, of all computations in the data market protocol including contribution assessment and outlier detection are verifiable through zero-knowledge proofs; and v) efficient and universal design. We propose a blockchain-based marketplace design to achieve all five objectives mentioned above. In our design, we utilize a distributed storage infrastructure and an aggregator aside from the project owner and the trainers. The aggregator is a processing node that performs certain computations, including assessing trainer contributions, removing outliers, and updating hyper-parameters. We execute the proposed data market through a blockchain smart contract. The deployed smart contract ensures that the project owner cannot evade payment, and honest trainers are rewarded based on their contributions at the end of training. Finally, we implement the building blocks of the proposed data market and demonstrate their applicability in practical scenarios through extensive experiments.


Published at 2023/02/27 02:10:48 (JST)

Verifiable Manufacturing Using Blockchain

我々は、製造プロセスの検証可能性を実現するためのブロックチェーンベースのソリューションを提案する。これは、元々クラウドコンピューティングのために開発されたもので、クライアントがより強力なサーバーに計算をアウトソースする際に、そのサーバーが正しく計算を実行したかどうかを信頼する必要がないようにするものです。検証可能なコンピューティングとは、クライアントが暗号オブジェクトを生成し、サーバーがそれを使って結果の正しさを検証する暗号的証明を生成できるようにすることで実現するものです。クラウドコンピューティングにおけるサーバのブラックボックス化は、上流企業の製造工程と類似している。本研究では、検証可能なコンピューティングを実現するために必要な、物理プロセスとそのデジタル表現である状態遷移の一対一の対応関係を構築する。この場合、検証可能なコンピューティングを直接適用することは計算量が膨大になるため、ブロックチェーンを導入し、物理プロセスに検証可能なコンピューティングを適用する計算量的に実現可能な方法論を提供する。Hyperledger Fabric上で開発したプルーフオブコンセプトに実装し、その結果を示す。

We propose a blockchain-based solution for enabling verifiability of manufacturing processes. We base our solution on the methodology of verifiable computing which, originally developed for cloud computing, enables clients to outsource computations to more powerful servers without the need to trust that the server correctly performed desired computation. Verifiable computing accomplishes this by enabling the client to generate cryptographic objects that the server must use to produce a cryptographic proof that verifies the correctness of results. The black box nature of servers in cloud computing is analogous to that of the manufacturing processes of an upstream manufacturer. In this work, we develop a one-to-one correspondence between physical processes and their digital representations as state sequences which is needed for the implementation of verifiable computing. Because direct application of verifiable computing in this case would be computationally prohibitive, we introduce a blockchain to provide a computationally feasible methodology for verifiable computing applied to physical processes. We implement and show the results of our implementation on a proof of concept, developed on Hyperledger Fabric.


Published at 2023/02/26 17:08:23 (JST)

Post Quantum Secure Blockchain-based Federated Learning for Mobile Edge Computing

モバイルエッジコンピューティング(MEC)は、移動中のデータの通信とエッジ処理のための有望なパラダイムである。我々は、Federated Learning (FL)とブロックチェーンの顕著な特徴をコネクテッド自律走行車のようなMECアーキテクチャに採用し、完全な分散化、不変性、報酬の仕組みを同時に実現することを目指している。FLは、大量のデータ通信の代わりにモデルの更新を中央ポイントに配信する必要があるため、接続性に制約のあるモバイルデバイスに有利である。例えば、自律的に接続された自動車におけるFLは、データの多様性を高め、モデルのカスタマイズを可能にし、自動車が(ローカルモデルを利用して)短時間接続されていない場合でも予測が可能である。しかし、既存の同期型FLやブロックチェーンは、モビリティに起因する障害により通信コストが極めて高く、MECネットワークに直接適用することはできません。我々は、BFL-MECと呼ばれる完全非同期型ブロックチェーン連携学習(BFL)フレームワークを提案し、モバイルクライアントとそのモデルが独立して進化しながら、グローバル学習プロセスの安定性が保証されるようにする。さらに重要な点として、我々はBFL-MECにポスト量子セキュア機能を採用し、クライアントのアイデンティティを検証し、悪意ある攻撃から防御します。我々の設計仮定と結果は全て、広範なシミュレーションによって評価されている。

Mobile Edge Computing (MEC) has been a promising paradigm for communicating and edge processing of data on the move. We aim to employ Federated Learning (FL) and prominent features of blockchain into MEC architecture such as connected autonomous vehicles to enable complete decentralization, immutability, and rewarding mechanisms simultaneously. FL is advantageous for mobile devices with constrained connectivity since it requires model updates to be delivered to a central point instead of substantial amounts of data communication. For instance, FL in autonomous, connected vehicles can increase data diversity and allow model customization, and predictions are possible even when the vehicles are not connected (by exploiting their local models) for short times. However, existing synchronous FL and Blockchain incur extremely high communication costs due to mobility-induced impairments and do not apply directly to MEC networks. We propose a fully asynchronous Blockchained Federated Learning (BFL) framework referred to as BFL-MEC, in which the mobile clients and their models evolve independently yet guarantee stability in the global learning process. More importantly, we employ post-quantum secure features over BFL-MEC to verify the client's identity and defend against malicious attacks. All of our design assumptions and results are evaluated with extensive simulations.


Published at 2023/02/25 22:57:47 (JST)

Privacy-Preserving Electricity Theft Detection based on Blockchain


In most electricity theft detection schemes, consumers' power consumption data is directly input into the detection center. Although it is valid in detecting the theft of consumers, the privacy of all consumers is at risk unless the detection center is assumed to be trusted. In fact, it is impractical. Moreover, existing schemes may result in some security problems, such as the collusion attack due to the presence of a trusted third party, and malicious data tampering caused by the system operator (SO) being attacked. Aiming at the problems above, we propose a blockchain-based privacy-preserving electricity theft detection scheme without a third party. Specifically, the proposed scheme uses an improved functional encryption scheme to enable electricity theft detection and load monitoring while preserving consumers' privacy; distributed storage of consumers' data with blockchain to resolve security problems such as data tampering, etc. Meanwhile, we build a long short-term memory network (LSTM) model to perform higher accuracy for electricity theft detection. The proposed scheme is evaluated in a real environment, and the results show that it is more accurate in electricity theft detection within acceptable communication and computational overhead. Our system analysis demonstrates that the proposed scheme can resist various security attacks and preserve consumers' privacy.