The popularity of blockchain technology has bootstrapped many “Web3” applications, e.g., Ethereum and IPFS, that apply distributed ledger technology to store transactions. The amount of transactions generated and stored in such Web3 applications is significant and, in its raw form, usually not searchable by users. Existing Web3 transaction indexing and search engines are predominantly centralized and, therefore, can manipulate search results or censor particular queries. With the proliferation of Web3 transactions and applications, a decentralized and censorship-resistant search primitive is becoming essential. We present DeScan, a decentralized and censorship-resistant indexing and search engine for Web3. Users index their local Web3 transactions using custom rules that output triplets. Generated triplets are bundled in a distributed transaction graph that is searchable by other users. To coordinate search and distribute the storage of the transaction graph over peers in the network, we build upon a Skip Graph (SG) data structure. Since the Skip Graph does not provide any resilience against adversarial peers that censor searches, we propose four modifications to improve its robustness. We implement DeScan and conduct experiments with up to 12 800 peers and 10 million Ethereum transactions. Our experiments show that DeScan with our modifications enabled can tolerate 20% adversarial peers and 35% unresponsive peers without disruption. Moreover, we find that searches in DeScan are usually completed well within a second, even when the network grows. Finally, we show that storage and network costs are evenly distributed amongst peers as the network grows.
The use of distributed data storage and management structures, such as Distributed Ledger Technologies (DLT), in the energy sector has gained great interest in recent times. This opens up new possibilities in e.g. microgrid management, aggregation of distributed resources, peer-to-peer trading, integration of electromobility or proof-of-origin strategies. However, in order to benefit from those new possibilities, new challenges have to be overcome. This work focuses on one of these challenges, which is the need to ensure interoperability when integrating DLT-enabled devices in energy use cases. Firstly, the use of DLTs in the energy sector will be analyzed and the main use cases will be presented. Then, a classification of DLT-Energy use cases will be proposed. Secondly, the need for a common reference architecture framework to analyze those use cases with a focus on interoperability will be discussed and the current activities in research and standardization in this field will be presented. Finally, a new common reference architecture framework based on current activities in standardization will be presented.
Due to the immutability of blockchain, many applications are emerging by providing trust to the trustless Internet. However, immutability becomes a weakness in some applications that require modification and deletion, such as personal information and SNS(Social Network Service), and cannot use blockchain technology. Therefore, in this paper, we propose a redactable blockchain scheme that can be used universally regardless of the consensus algorithms and blockchain types. In addition, without using a heavy cryptographic algorithm, and needing to re-mine, the proposed scheme can delete and modify content in the ledger, so it is efficient. Moreover, the proposed scheme can modify and delete at the transaction level. Additionally, the proposed scheme supports encryption for protecting the privacy and there is no need to save the original content after modification or deletion.
Open access
Blockchain Technology Applications and Security
Caching and Content Delivery
Advanced Steganography and Watermarking Techniques
Nana Kwadwo Akrasi‐Mensah, Andrew Selasi Agbemenu, Henry Nunoo‐Mensah, Eric Tutu Tchao · 9 authors
Blockchain-IIoT integration into industrial processes promises greater security, transparency, and traceability. However, this advancement faces significant storage and scalability issues with existing blockchain technologies. Each peer in the blockchain network maintains a full copy of the ledger which is updated through consensus. This full replication approach places a burden on the storage space of the peers and would quickly outstrip the storage capacity of resource-constrained IIoT devices. Various solutions utilizing compression, summarization or different storage schemes have been proposed in literature. The use of cloud resources for blockchain storage has been extensively studied in recent years. Nonetheless, block selection remains a substantial challenge associated with cloud resources and blockchain integration. This paper proposes a deep reinforcement learning (DRL) approach as an alternative to solving the block selection problem, which involves identifying the blocks to be transferred to the cloud. We propose a DRL approach to solve our problem by converting the multi-objective optimization of block selection into a Markov decision process (MDP). We design a simulated blockchain environment for training and testing our proposed DRL approach. We utilize two DRL algorithms, Advantage Actor-Critic (A2C), and Proximal Policy Optimization (PPO) to solve the block selection problem and analyze their performance gains. PPO and A2C achieve 47.8% and 42.9% storage reduction on the blockchain peer compared to the full replication approach of conventional blockchain systems. The slowest DRL algorithm, A2C, achieves a run-time 7.2 times shorter than the benchmark evolutionary algorithms used in earlier works, which validates the gains introduced by the DRL algorithms. The simulation results further show that our DRL algorithms provide an adaptive and dynamic solution to the time-sensitive blockchain-IIoT environment.
Sergiu Lupaiescu, Petru Cioată, Cristina Elena Turcu, Cristina Elena Turcu · 8 authors
Decentralized databases have gained popularity in the last few years in different areas, such as: traceability, supply chains or finance. Leveraging this type of emerging technology will improve knowledge sharing, as well as the transparency and traceability of the data for digital systems. In a similar way, the characteristics are advertised by the centralized ledger technologies, which are manufactured by large cloud service providers such as Amazon. The present study analyzes the performance of two ledger technologies: BigchainDB (i.e., the decentralized blockchain database) and Amazon QLDB (i.e., the centralized ledger database with transparent and immutable characteristics). For the purposes of comparison, we have integrated these technologies into our traceability platform, which is called the Smart Tracking Platform (STP), and performed a series of experiments enabling us to acquire data for different metrics, such as CPU or memory usage for both the reading and writing operations. The findings of the present study show that QLDB has an overall better performance compared to BigchainDB, based on the metrics that have been considered. From the perspective of database ledger implementation, Amazon QLDB proved to be an integrated solution, easier to use, while BigchainDB comprises a more complex system to be implemented and developed, but is more flexible. Although both systems are almost ready to use solutions for local environments, when it comes to configuration and setting up the communication between nodes within a production environment, BigchainDB adds a layer of complexity from a DevOps perspective, while Amazon QLDB completely overcomes it. Depending on the area considered and the identified needs, both BigchainDB and Amazon QLDB can be considered as suitable solutions for a ledger database.
Aiming at the transaction problem of multi-source heterogeneous distribution network, a P2P intelligent contract based on blockchain technology is proposed. Firstly, a multi-source heterogeneous distribution network model based on Intelligent contract is established. Secondly, a multi-source heterogeneous distribution network market transaction mechanism is proposed. The mechanism designs different kinds of transaction members, frameworks and processes. Transaction members can participate in the market quotation and determine the transaction unit price according to their own power surplus and shortage state. Finally, a smart contract solution with blind beat mechanism is designed for the proposed transaction mechanism. The effectiveness of the transaction mechanism is verified by an example and deployed on the Ethereum private chain. The effectiveness of the transaction mechanism is verified by an example and deployed on the Ethereum private chain. Through the simulation transaction analysis, it can be seen that the above transaction mechanism effectively improves the economic benefits of trading members and effectively ensures the market security and free competition.
Compact block, which replaces transactions in the block with their hashes, is an effective means to speed up block propagation in the Bitcoin network. The compact block mechanism in Bitcoin counts on the fact that many nodes may already have the transactions (or most of the transactions) in the block, therefore sending the complete block containing the full transactions is unnecessary. This fact, however, does not hold in the Ethereum network. Adopting compact block directly in Ethereum may degrade the block propagation speed significantly because the probability of a node not having a transaction in the sending block is relatively high in Ethereum and requesting the missing transactions after receiving the compact block takes much additional time. To investigate the factors that prevent compact block in Ethereum, we set up probe nodes to collect data from Ethereum MainNet and performed data analysis. Our analysis results indicate that the missing transactions could be attributed to factors such as small transaction pools, network latency, and miners' selfish behaviors. Moreover, simply enlarging the transaction pool and using the prediction algorithm proposed for Bitcoin to predict the missing transactions and prefetch them do not work for Ethereum. This article proposes hybrid-compact block (HCB), an efficient compact block propagation scheme for Ethereum and other similar blockchains. First, we develop a Secondary Pool to store the low-fee transactions, which are removed from the primary transaction pool, to conserve storage space. As simple auxiliary storage, the Secondary Pool does not affect the normal block processing of the primary pool in Ethereum. Second, we design a machine learning-based transaction prediction module to precisely predict the missing transactions caused by network latency and selfish behaviors. We implemented our HCB scheme and other compact-block-like schemes (as benchmarks) and deployed a number of worldwide nodes over Ethereum MainNet to experimentally investigate them. Experimental results show that HCB performs best among the existing compact-block-like schemes and can reduce propagation time by more than half with respect to the current block propagation scheme in Ethereum.
The right to vote is one of the fundamental tenets upon which democracies are built. The voting process has several difficulties in the modern day due to the prevalence of digital technology. By developing a prototype application that makes use of the idea of a ledger-based data store on a blockchain and a graph database, the purpose of this paper is to search for a workable answer to the problems of security, accessibility, and transparency in the electoral process, in an effort to identify an answer that is best suited and adaptable on a large scale. A distributed ledger uses linked nodes to store data in such a way that once a block is written, it cannot be modified on the chain without compromising the chain's integrity and the trust that users have placed in it. This property of blockchain is utilised by us in developing a secure data store for the application.
K Vinodha, R. Jayashree, Geethika Kommineni, Manali Tanna · 5 authors
Due to the persistent issue of blockchain scala-bility, sharding was established as a database splitting approach utilized by blockchain systems to improve scalability. Sharding in blockchain systems presents several challenges, including security, cross-shard communication, and scalability. A significant quantity of study has been conducted in these sub-areas. However, no new research has been conducted that looks deeper into the issues in each area. This survey provides a concise overview of current concepts and challenges in sharded blockchain systems. We explore distributed systems, blockchain technology, sharding and related concepts. We analyzed 14 papers and divided the findings into two categories: concepts and challenges. The following is how the paper is organized: The first section introduces the concepts of sharding, distributed systems, and blockchain technology, the following sections discuss the challenges and relevant algorithms. Finally, we compare the challenges to present results.
We propose a service-aware dynamic sharding approach for enhancing the scalability of blockchain platforms. The objective of our proposed approach is to decrease the service latency for user transactions and increase the transaction throughput of conventional blockchain platforms. Sharding is a well-known solution to the problem of blockchain scalability. In sharded blockchains, transactions can be processed in parallel on different shards. However, compared to intra-transactions, cross-shard transactions, which are inevitably generated in sharded blockchains, are confirmed after a relatively long time. This attribute may result in the overall degradation of performance. To mitigate the effects of cross-shard transactions on the performance of blockchain systems, our proposed approach dynamically relocates the data accessed through cross-shard transactions to the same shard. Further, two or more highly related shards are adaptively merged into a single shard, or a single shard is split into smaller disjointed shards to fully utilize shards in parallel. To verify the efficacy of our proposed approach, we implemented a sharded blockchain using the Hyperledger-Fabric platform based on the design concepts of existing sharded blockchains. The experimental results show that the proposed approach can improve the scalability of existing blockchains while maintaining the consistency of ledgers during dynamic state changes.
The scalability problem has been one of the most significant barriers limiting the adoption of blockchains. Blockchain sharding is a promising approach to this problem. However, the sharding mechanism introduces a significant number of cross-shard transactions, which are expensive to process. This paper focuses on the transaction allocation problem to reduce the number of cross-shard transactions for better scalability. In particular, we systematically formulate the transaction allocation problem and convert it to the community detection problem on a graph. A deterministic and fast allocation scheme TxAllo is proposed to dynamically infer the allocation of accounts and their associated transactions. It directly optimizes the system throughput, considering both the number of cross-shard transactions and the workload balance among shards. We evaluate the performance of TxAllo on an Ethereum dataset containing over 91 million transactions. Our evaluation results show that for a blockchain with 60 shards, TxAllo reduces the cross-shard transaction ratio from 98% (by using traditional hash-based allocation) to about 12%. In the meantime, the workload balance is well maintained. Compared with other methods, the execution time of TxAllo is almost negligible. For example, when updating the allocation every hour, the execution of TxAllo only takes 0.5 seconds on average, whereas other concurrent works, such as BrokerChain (INFOCOM'22) leveraging the classic METIS method, require 422 seconds.
Limitations on high latency and low scalability of classical blockchain systems retard their adoptions and applications. Reconstructed blockchain systems have been proposed to avoid the consumption of competitive transactions caused by linear sequenced blocks. These systems, instead, structure transactions/blocks in the form of Directed Acyclic Graph (DAG) and consequently rebuild upper layer components. The promise of DAG-based blockchain systems is to enable fast confirmation (complete transactions within million seconds) and high scalability (attach transactions in parallel) without significantly compromising security. However, this field still lacks systematic work that summarises DAG techniques. To bridge the gap, this Systematization of Knowledge (SoK) provides a comprehensive analysis of ever-existing and ongoing DAG-based blockchain systems. We abstract a general model to capture the main features and identify six types of design patterns. Then, we evaluate these systems from the perspectives of structure, consensus, property, security, and performance. We further discuss the trade-off between different factors, open challenges, and the potentiality of DAG-based solutions, indicating their promising directions for future research.
This paper proposes a solution to the transfer problem between blockchain-based heterogeneous cryptocurrencies and CBDCs, with research derived from an analysis of the existing literature. Interoperability between heterogeneous blockchains has been an obstacle to service diversity and user convenience. Many types of cryptocurrencies are currently trading on the market, and many countries are researching and testing central bank digital currencies (CBDCs). In this paper, existing interoperability studies and solutions between heterogeneous blockchains and differences from the proposed service model are described. To enhance digital financial services and improve user convenience, transfer between heterogeneous cryptocurrencies, transfer between heterogeneous CBDCs, and transfer between cryptocurrency and CBDC should be required. This paper proposes an interoperable architecture between heterogeneous blockchains, and a decentralized peer-to-peer (P2P) service model based on the interoperable architecture for transferring between blockchain-based heterogeneous cryptocurrencies and CBDCs. Security threats to the proposed service model are identified and security requirements to prevent the identified security threats are specified. The mentioned security threats and security requirements should be considered when implementing the proposed service model.
Decentralized Storage Networks (DSNs) can gather storage resources from mutually untrusted providers and form worldwide decentralized file systems. Compared to traditional storage networks, DSNs are built on top of blockchains, which can incentivize service providers and ensure strong security. However, existing DSNs face two major challenges. First, deduplication can only be achieved at the directory-level. Missing file-level deduplication leads to unavoidable extra storage and bandwidth cost. Second, current DSNs realize file indexing by storing extra metadata while blockchain ledgers are not fully exploited. To overcome these problems, we propose FileDAG, a DSN built on DAG-based blockchain to support file-level deduplication in storing multi-versioned files. When updating files, we adopt an increment generation method to calculate and store only the increments instead of the entire updated files. Besides, we introduce a two-layer DAG-based blockchain ledger, by which FileDAG can provide flexible and storage-saving file indexing by directly using the blockchain database without incurring extra storage overhead. We implement FileDAG and evaluate its performance with extensive experiments. The results demonstrate that FileDAG outperforms the state-of-the-art industrial DSNs considering storage cost and latency.
Blockchain and Internet of Things (IoT) have become one of the most researched topics in recent years. The application areas of both these fields are quite broad and one can complement the other in bringing in the best possible outcome. Keeping that in mind, this paper proposed how Blockchain can be utilized to provide a more secure and improved IoT ecosystem where the components of the ecosystem will be more protected and less susceptible to unwanted intrusions. We also considered using InterPlanetary File System (IPFS) and Hyperledger Fabric as a means of IoT data storage, which can ensure better protection compared to centralized cloud storage. We have also utilized Ethereum Smart Contracts (SC) for Proof of Concept deployment of our model. The experimental outcome as well as the cost and security analysis of our deployed Smart Contracts suggest that it is more beneficial to use Blockchain and distributed storage systems to safeguard the IoT ecosystem and its data.
User identification in decentralized systems is a demanding task. Identification systems should work resiliently and have efficient performance. Moreover, identification systems should protect the data that they must store against hackers and saboteurs. Keeping a system with decentralized identification without any intervention in the middle has attracted attention to improve earlier centralized identification systems. Decentralized Identifiers (DIDs) constitute a solution for identification divided into different modules. The verifiable data registry is one of the main parts of this technology, which is distributed storage of identity properties. We analyze the decentralized identification data registry and compare the performance of verifiable data registry based on blockchain and the Distributed Hash Table (DHT) on different scales of systems. Our evaluation results show that DHT has better performance. Furthermore, a model based on DHT shows that in addition to immutable storage and faster query time, it makes systems handle or search in data storage with lower searching time compared to Ethereum Blockchain as another immutable secure technology. Finally, our results show that DHT is a better solution than other models in different scenarios. Although blockchain has promising results on a small scale, it still has problems with storage and query time in large-scale systems.
J. D. Preece, Christopher J. Morris, John M. Easton
The System for Ticketing Ubiquity with Blockchains (STUB) is a novel solution to multi-modal transport ticketing. Introduced previously using Hyperledger Fabric, STUB utilises the distributed mechanics of blockchain technology right at the core of its architecture, allowing stakeholders from different transport modes to vend and validate tickets on a shared ledger. This open approach to ticketing data will benefit transport governing bodies, transport operators, and passengers alike by ensuring cross-party cooperation and presenting a fresh holistic approach to the ticketing sector. This paper addresses issues from STUB 1.0, concerning validating tickets for a multi-modal transport system. To overcome this, we propose creating a graph structure, known as the Transport Network Graph (TNG), to represent the transport network with all of the services provided by the Transport Service Providers (TSPs). This enables the implementation of an automated Revenue Allocation System (RAS), whilst retaining the benefits provided by blockchain technology.
GasTokens are created by smart contracts executing in the Ethereum blockchain to support a form of transaction fee pre-payment. Even though GasTokens had a period of significant activity on Ethereum (regularly surpassing half of the overall weekly smart contract creation and destruction activities), few systematic studies have been conducted on GasToken usage and its effect on the blockchain network. This paper focuses on understanding the adoption of GasTokens on Ethereum since May of 2020. We first analyze the usage patterns, including the creation, destruction, and holding of GasTokens, then report several price findings related to GasTokens, and compare the fees paid by users submitting transactions that create and destroy GasTokens to the fees paid by all the transactions in the network over different time periods. We characterize the benefits obtained by GasToken transaction senders and report the impact of GasToken creations and destructions on the major mining pools.
Muhammad Habib ur Rehman, Emanuel Figetakis, Yahuza Bello, Charlie Obimbo
The potential of having multiple distributed applications across multiple domains such as healthcare, finance, supply chain management and many more have made blockchain very popular among both academia and industries. Blockchain provides the much-needed mechanism for decentralization of systems, where the need of trusted central authority is eliminated. Proof of Work (PoW) is heavily adopted in both Bitcoin and Ethereum based blockchain, where many miners (or mining pools) compete to mine each block generated by solving a cryptographic puzzle that uses all of the previous information of the blockchain, before tying the block to the blockchain with the nonce. Recently there is a shift in having two or more mining pools for the PoW consensus in Ethereum-based blockchain. Majority of the studies conducted for multiple mining pool techniques in the literature are verified with simulation experiments. Therefore, in this paper, we implement a testbed for Ethereum blockchain with multiple nodes that simulate two mining pools using PoW consensus in a centralized and decentralized fashion. Two miner-nodes were deployed with different computational power (in term of CPU threads) and transactions executed. We evaluate the contribution of each miner node in the blockchain system and the assignment of transactions with respect to the computational resources available.
Web3 aims at creating a decentralized platform that is competitive with modern cloud infrastructures that support today's Internet. However, Web3 is still limited, supporting only applications in the domains of content creation and sharing, decentralized financing, and decentralized communication. This is mainly due to the technologies supporting Web3: blockchain, IPFS, and libp2p, that although provide a good collection of tools to develop Web3 applications, are still limited in terms of design and performance. This motivates the need to better understand these technologies as to enable novel optimizations that can push Web3 to its full potential. Unfortunately, understanding the current behavior of a fully decentralized large-scale distributed system is a difficult task, as there is no centralized authority that has full knowledge of the system operation. To this end, in this paper we characterize the workload of IPFS, a key enabler of Web3. To achieve this, we have collected traces from accesses performed by users to one of the most popular IPFS gateways located in North America for a period of two weeks. Through the fine analysis of these traces, we gathered the amount of requests to the system, and found the providers of the requested content. With this data, we characterize both the popularity of requested and provided content, as well as their geo-location (by matching IP address with the MaxMind database). Our results show that most of the requests in IPFS are only to a few different content, that is provided by large portion of peers in the system. Furthermore, our analysis also shows that most requests are provided by the two largest portions of providers in the system, located in North America and Europe. With these insights, we conclude that the current IPFS architecture is sub-optimal and propose a research agenda for the future.
The proliferation of resource-constrained devices has become prevalent across various digital applications, including smart homes, smart healthcare, and smart transportation, among others. However, the integration of these devices brings many security issues. To address these concerns, Blockchain technology has been widely adopted due to its robust security characteristics, including immutability, cryptography, and distributed consensus. However, implementing blockchain within these networks is highly challenging due to the limited resources of the employed devices and the resource-intensive requirements of the blockchain. To overcome these challenges, a multitude of researchers have proposed lightweight blockchain solutions specifically designed for resource-constrained networks. In this paper, we present a taxonomy of lightweight blockchain solutions proposed in the literature. More precisely, we identify five areas within the "lightweight" concept, namely, blockchain architecture, device authentication, cryptography model, consensus algorithm, and storage method. We discuss the various methods employed in each "lightweight" category, highlighting existing gaps and identifying areas for improvement. Our review highlights the missing points in existing systems and paves the way to building a complete lightweight blockchain solution for networks of resource-constrained devices.