Smart contract (SC) is a user-defined program code over blockchain, which holds the characteristics of immutability and auditability without requiring trust third party and is crucial to provide in-network computation for green applications. Herein we investigate the interactions among the SCs, where the functions defined in one SC are called by another one. The existing work, Ethereum name service (ENS), provides a method to map human-readable names to machine-readable addresses. However, it still suffers the problems induced from the ossification of SC, such as no mechanism to call functions in a non-existing SC, to update SC, to acquire the SC information (e.g. contract application binary interface and address), and to achieve access control. To solve these problems, we propose a flexible smart contract interaction framework with access control (FSCC), where SC name and information are separately stored at blockchain and the distributed off-chain storage to reduce on-chain storage overhead. With the FSCC, interactions with non-existing SC, update of SC, and access control of SC can be achieved. Furthermore, performance evaluations show that on-chain storage overhead can be greatly reduced with keeping the communication delay at a low level.
With the advent of the Internet, the gaming industry has grown tremendously in business, which also raises concerns for cheating and unfair gameplay. In this paper, we propose a novel approach (GiNA) using Blockchain technology to address a few problems with online Peer-to-Peer (P2P) games. GiNA uses two different data packet transfer schemes to ensure the security and authenticity of the data packet sent and received by game clients. More sensitive data uses a Smart contract-based ON-CHAIN data packet transfer solution and less sensitive data uses an OFF-CHAIN data packet transfer solution with end-to-end encryption for data security. A marketplace where peers can buy and sell purchasable assets with the help of Gicoins. Gicoins is a stable token with compliance with the ERC 20 token of Etheruem Blockchain. Later, a low cost and low bandwidth utilization data storage solution is proposed for storing data in a decentralized and distributed manner. Results show that the performance of the proposed approach GiNA is better in comparison to the traditional approaches with parameters such as latency, scalability, packet loss percentage, Blockchain (BC) performance, and data storage comparison.
Periklis Kostamis, Andreas Sendros, Pavlos S. Efraimidis
The cost of using a blockchain infrastructure as well as the time required to search and retrieve information from it must be considered when designing a decentralized application. In this work, we examine a comprehensive set of data management approaches for Ethereum applications and assess the associated cost in gas as well as the retrieval performance. More precisely, we analyze the storage and retrieval of various-sized data, utilizing smart contract storage. In addition, we study hybrid approaches by using IPFS and Swarm as storage platforms along with Ethereum as a timestamping proof mechanism. Such schemes are especially effective when large chunks of data have to be managed. Moreover, we present methods for low-cost data handling in Ethereum, namely the event-logs, the transaction payload, and the almost surprising exploitation of unused function arguments. Finally, we evaluate these methods on a comprehensive set of experiments.
It is widely accepted that blockchain systems cannot execute calls to external systems or services due to each node having to reach a deterministic state. However, in this paper we show that this belief is preconceived by demonstrating a method that enables blockchain and distributed ledger technologies to perform calls to external systems initiated from the blockchain/DLT itself.
LightChain is the first Distributed Hash Table (DHT)-based blockchain with a logarithmic asymptotic operational complexity, and a distributed storage layer, which preserves its integrity under the corrupted majority power of nodes. Running smart contract-based transactions, however, was a missing feature in the original implementation of LightChain. In this demo paper, we present the software architecture of our open-source smart contract-enabled test network for LightChain.
The peer-to-peer (P2P) network of blockchain used to transport its transactions and blocks has a high impact on the efficiency and security of the system. The P2P network topologies of popular blockchains such as Bitcoin and Ethereum, therefore, deserve our highest attention. The current Ethereum blockchain explorers (e.g., Etherscan) focus on the tracking of block and transaction records but omit the characterization of the underlying P2P network. This work presents the Ethereum Network Analyzer (Ethna), a tool that probes and analyzes the P2P network of the Ethereum blockchain. Unlike Bitcoin that adopts an unstructured P2P network, Ethereum relies on the Kademlia DHT to manage its P2P network. Therefore, the existing analytical methods for Bitcoin-like P2P networks are not applicable to Ethereum. Ethna implements a novel method that accurately measures the degrees of Ethereum nodes. Furthermore, it incorporates an algorithm that derives the latency metrics of message propagation in the Ethereum P2P network. We ran Ethna on the Ethereum Mainnet and conducted extensive experiments to analyze the topological features of its P2P network. Our analysis shows that the Ethereum P2P network possesses a certain effect of small-world networks, and the degrees of nodes follow a power-law distribution that characterizes scale-free networks.
In a corpus of 45,821 app reviews of the top five mobile cryptocurrency wallets, we identified and qualitatively analyzed 6,859 reviews pertaining to the user experience (UX) with those wallets. Our analysis suggests that both new and experienced users struggle with general and domain-specific UX issues that, aside from frustration and disengagement, might lead to dangerous errors and irreversible monetary losses. We reveal shortcomings of current wallet UX as well as users’ misconceptions, some of which can be traced back to a reliance on their understanding of conventional payment systems. For example, some users believed that transactions were free, reversible, and could be canceled anytime, which is not the case in reality. Correspondingly, these beliefs often resulted in unmet expectations. Based on our findings, we provide recommendations on how to design cryptocurrency wallets that both alleviate the identified issues and counteract some of the misconceptions in order to better support newcomers.
Designing blockchain-based applications is a challenging task and requires a number of coordinated architecture decisions. To guide decision making in this regard, we systematically explore this architectural design space and possible solution strategies. More precisely, we provide architectural design decisions and decision options in terms of patterns and practices. Our research shows that most design decisions are influenced by the need to offset current blockchain drawbacks such as scalability, privacy, and usability by using centralized elements. This suggests that a hybrid architecture is beneficial in many design situations.
Since its advent in 2009, Bitcoin, a cryptography-enabled peer-to-peer digital payment system, has been gaining increasing attention from both academia and industry. An effort designed to overcome a cluster of bottlenecks inherent in existing centralized financial systems, Bitcoin has always been championed by the crypto community as an example of the spirit of decentralization. While the decentralized nature of Bitcoin's Proof-of-Work consensus algorithm has often been discussed in great detail, no systematic study has so far been conducted to quantitatively measure the degree of decentralization of Bitcoin from an asset perspective -- How decentralized is Bitcoin as a financial asset? We present in this paper the first systematic investigation of the degree of decentralization for Bitcoin based on its entire transaction history. We proposed both static and dynamic analysis of Bitcoin transaction network with quantifiable decentralization measures developed based on network analysis and market efficiency study. Case studies are also conducted to demonstrate the effectiveness of our proposed metrics.
Bitcoin is a virtual and decentralized cryptocurrency that operates in a peer-to-peer network providing a private payment mechanism. It is a multi-billion dollar cryptocurrency, and hundreds of other cryptocurrencies are created based on it. Bitcoin is based on open source software (OSS) development. This paper presents the first comprehensive study of the Bitcoin ecosystem in GitHub organized around 481 most popular and actively developed Bitcoin related projects over eight years (2010-2018). Our work includes manual categorization of the projects, defining software health metrics, classification of projects according to these health metrics, and evaluation of the health trends of the ecosystem. The main findings suggest that the Bitcoin ecosystem in GitHub is represented by nine categories of projects. Moreover, the health of the majority of the projects is assessed as “Low Risk”.
Distributed Ledger Technologies (DLT) and Decentralized File Storages (DFS) are becoming increasingly used to create common, decentralized and trustless infrastructures where participants interact and collaborate in Peer-to-Peer interactions. A prominent use case is represented by decentralized data marketplaces, where users are consumers and providers at the same time, and trustless interactions are required. However, data in DLTs and DFS are usually unstructured and there are no efficient mechanisms to query a certain type of data for the search in the market. In this paper, we propose the use of a Distributed Hash Table (DHT) as a layer on top of DLTs where, once the data are acquired and stored in the ledger, these can be searched through multiple keyword based queries, thanks to the lookup functionalities offered by the DHT. The DHT network is a hypercube overlay structure, organized for an efficient processing of multiple keyword-based queries. We provide the architecture of such solution for a decentralized data marketplace and an analysis based on a simulation that proves the viability of the proposed approach.
As an append-only distributed database, blockchain is utilized in a vast variety of applications including the cryptocurrency and Internet-of-Things (IoT). The existing blockchain solutions show downsides in communication and storage scalability, as well as decentralization. In this article, we propose LightChain , which is the first blockchain architecture that operates over a Distributed Hash Table (DHT) of participating peers. LightChain is a permissionless blockchain that provides addressable blocks and transactions within the network, which makes them efficiently accessible by all peers. Each block and transaction is replicated within the DHT of peers and is retrieved in an on-demand manner. Hence, peers in LightChain are not required to retrieve or keep the entire ledger. LightChain is fair as all of the participating peers have a uniform chance of being involved in the consensus regardless of their influence such as hashing power or stake. We provide formal mathematical analysis and experimental results (simulations and cloud deployment) to demonstrate the security, efficiency, and fairness of LightChain , and show that LightChain is the only existing blockchain that can provide integrity under the corrupted majority power of peers. As we experimentally demonstrate, compared to the mainstream blockchains such as Bitcoin and Ethereum, LightChain requires around 66 times smaller per node storage, and is around 380 times faster on bootstrapping a new node to the system, and each LightChain node is rewarded equally likely for participating in the protocol.
Distributed Ledger Technologies (DLTs) have become an important driving force towards the creation of novel distributed applications aimed at solving problems that range from digital currency tools to self governing digital democracy systems. Our thesis is that Satoshi cryptocurrencies, i.e., Bitcoin and its variants, can be used to endow several popular distributed services with strong privacy, anonymity and censorship resistance properties that evade current solutions. To this end, we first study the design of Satoshi cryptocurrency mining protocols, and discover and document privacy and integrity vulnerabilities of Stratum, the de-facto pooled mining protocol. We have developed tools that exploit these vulnerabilities and have measured their impact and effectiveness under a rigorous academic context. Further, we have designed and implemented Bedrock, a solution that addresses these vulnerabilities. We have evaluated Bedrock in the live Bitcoin ecosystem and show that it achieved orders of magnitude better performance than traditional solutions like TLS and blanket encryption. We further introduce DLSS, a censorship-resistant, distributed ledger storage system that embeds client content into Satoshi transactions and organize it for fast search, recovery and reconstruction among hundreds of millions of financial transactions. DLSS distinguishes and exploits the singularities of different types of communications under censorship conditions. We design, implement and evaluate novel smart contracts tailored to the needs of censored users. For instance, we introduce difficult to censor and undetectable techniques to embed small quantities of data on Satoshi transactions, to be used for communications flowing out of the censored area that need to avoid detection by all-powerful censors. We also introduce techniques that prioritize cost optimization for storing large content flowing into the censored area, where uncensorability is the only priority. Further, we leverage our blockchain-writing constructs to introduce a novel perspective for traditionally hard problems of censorship resistance, private e-mail and secure port-knocking with surreptitious authentication and logging. We prove the security, privacy and anonymity of our smart contracts, and argue they impose unpalatable collateral damage to would-be censors. We build a monitoring and instrumentation framework for evaluating our constructs in the Litecoin cryptocurrency. We evaluate our blockchain-writing constructs by persisting hundreds of MBs of BBC news articles and censored software in the live Litecoin blockchain, where they are available to access for free anywhere in the world. We show that our solutions achieve storage throughput, blockchain utilization, and cost efficiency that improve by 2-4 orders of magnitude on state-of-the-art blockchain-writing solutions.
Currently, the P2P method is that its software runs on a P2P hardware environment. However, the software is not a P2P one. It is difficult to match the scenarios in which the users’ requirements change often. Meanwhile, if the software is out of service, all participants are affected. Thus, in this paper, we propose the fully decentralized application model, in which a P2P software runs in a P2P hardware environment. It is based on the blockchain, as a blockchain provides a secured P2P hardware environment. We focus on its P2P software (the P2P smart contract). A P2P smart contract is formed by smart contracts from its participants instead of a third party. It allows each participant to specify its requirement in a turning-complete way and the failure of one smart contract does not affect other smart contracts. We first describe the requirement of the P2P smart contract and the dependence among them. Then, we propose different ways to pair associated smart contracts. At last, we verify the proposed P2P smart contract model, and it shows more flexibility and robustness than the centralized software method.
Abstract Practical Byzantine Fault-tolerant Algorithm (PBFT) is the most widely used consensus algorithm in alliance chain, which has the advantages of fault tolerance and large throughput. However, PBFT also has some problems that can’t be ignored in specific blockchain applications, such as bad behavior of master node, high network communication overhead and low system flexibility. In this paper, the improvement measures of PBFT consensus algorithm are summarized from many aspects, and then compared with traditional PBFT algorithm. Finally, the development direction and trend of PBFT algorithm are prospected, hoping to provide reference for the research and innovation of PBFT consensus algorithm in the future.
David Yakira, Avi Asayag, Gad Cohen, Ido Grayevsky · 7 authors
We presentHelix, a blockchain-based consensus protocol forfairordering of transactions among nodes in a distributed network. Helix advances in rounds, in each an elected primary node proposes a potential block (a successive set of transactions). For being included in the blockchain, a block must pass validation by an elected committee of nodes. Nodes have two primary preferences. First, to be elected as committee members. Additionally, because each transaction is associated with one of the network nodes, nodes would like to prioritize their own transactions over those of others. Our definition of fairness incorporates three key elements. First, the process of electing nodes to committees is random and unpredictable. Second, a correlated sampling scheme is used to guarantee random selection and ordering of pending transactions in blocks. Third, transactions are encrypted to hide their associations with nodes and prevent censorship. Through the corresponding threshold decryption process we obtain an unpredictable and non-manipulable randomness beacon, which serves both the election process and the correlated sampling scheme. We define a quantitative measure of fairness in the protocol, prove theoretically that fairness manipulation in Helix is significantly limited, and present experiments evaluating fairness in practice.
Matthias Grundmann, Hedwig Amberg, Hannes Hartenstein
Bitcoin is based on a P2P network that is used to propagate transactions and blocks. While the P2P network design intends to hide the topology of the P2P network, information about the topology is required to understand the network from a scientific point of view. Thus, there is a natural tension between the 'desire' for unobservability on the one hand, and for observability on the other hand. On a middle ground, one would at least be interested on some statistical features of the Bitcoin network like the number of peers that participate in the propagation of transactions and blocks. This number is composed of the number of reachable peers that accept incoming connections and unreachable peers that do not accept incoming connections. While the number of reachable peers can be measured, it is inherently difficult to determine the number of unreachable peers. Thus, the number of unreachable peers can only be estimated based on some indicators. In this paper, we first define our understanding of unreachable peers and then propose the PAL (Passive Announcement Listening) method which gives an estimate of the number of unreachable peers by observing ADDR messages that announce active IP addresses in the network. The PAL method allows for detecting unreachable peers that indicate that they provide services useful to the P2P network. In conjunction with previous methods, the PAL method can help to get a better estimate of the number of unreachable peers. We use the PAL method to analyze data from a long-term measurement of the Bitcoin P2P network that gives insights into the development of the number of unreachable peers over five years from 2015 to 2020. Results show that about 31,000 unreachable peers providing useful services were active per day at the end of the year 2020. An empirical validation indicates that the approach finds about 50 % of unreachable peers that provide useful services.
Dániel Kondor, Nikola Bulatovic, József Stéger, István Csabai · 5 authors
Bitcoin and Ethereum transactions present some of the largest real-world complex networks that are publicly available for study, including a detailed picture of their time evolution. As such, they have received a considerable amount of attention from the network science community along with analyses from economic and cryptographic perspectives. Among these studies, in an analysis on the early instance of the Bitcoin network, we have shown the clear presence of the preferential attachment, or the “rich-get-richer” phenomenon. Now, we revisit this question, using a recent version of the Bitcoin network that has grown almost 100-fold since our original analysis. Furthermore, we additionally carry out a comparison with Ethereum, the second most important cryptocurrency. Our results show that preferential attachment continues to be a key factor in the evolution of both the Bitcoin and Ethereum transactoin networks. To facilitate further analysis, we publish a recent version of both transaction networks, and an efficient software implementation that is able to evaluate linking statistics necessary for learn about preferential attachment on networks with several hundred million edges.
Dániel Kondor, Nikola Bulatović, József Stéger, István Csabai · 5 authors
Bitcoin and Ethereum transactions present one of the largest real-world\ncomplex networks that are publicly available for study, including a detailed\npicture of their time evolution. As such, they have received a considerable\namount of attention from the network science community, beside analysis from an\neconomic or cryptography perspective. Among these studies, in an analysis on\nthe early instance of the Bitcoin network, we have shown the clear presence of\nthe preferential attachment, or "rich-get-richer" phenomenon. Now, we revisit\nthis question, using a recent version of the Bitcoin network that has grown\nalmost 100-fold since our original analysis. Furthermore, we additionally carry\nout a comparison with Ethereum, the second most important cryptocurrency. Our\nresults show that preferential attachment continues to be a key factor in the\nevolution of both the Bitcoin and Ethereum transactoin networks. To facilitate\nfurther analysis, we publish a recent version of both transaction networks, and\nan efficient software implementation that is able to evaluate linking\nstatistics necessary for learn about preferential attachment on networks with\nseveral hundred million edges.\n
Peer-to-peer (p2p) content delivery is promising to reduce the cost of traditional CDNs and complement the decentralized storage networks such as Filecoin. However, reliable p2p delivery requires proper enforcement of delivery fairness, i.e., the deliverers should be rewarded according to their in-time delivery. Unfortunately, most existing studies on delivery fairness are based on non-cooperative game-theoretic assumptions that are arguably unrealistic in the ad-hoc p2p setting. We for the first time put forth the expressive yet still minimalist securities for p2p content delivery, and give two efficient solutions FairDownload and FairStream via the blockchain for p2p downloading and p2p streaming scenarios, respectively. Our designs not only guarantee delivery fairness to ensure deliverers be paid (nearly) proportional to his in-time delivery, but also ensure the content consumers and content providers to be fairly treated. The fairness of each party can be guaranteed when the other two parties collude to arbitrarily misbehave. Moreover, the systems are efficient in the sense of attaining asymptotically optimal on-chain costs and optimal deliverer communication. We implement the protocols to build the prototype systems atop the Ethereum Ropsten network. Extensive experiments done in LAN and WAN settings showcase their high practicality.
Alex Auvolat, Yérom-David Bromberg, Davide Frey, François Taı̈ani
Recent works have proposed new Byzantine consensus algorithms for blockchains based on epidemics, a design which enables highly scalable performance at a low cost. These methods however critically depend on a secure random peer sampling service: a service that provides a stream of random network nodes where no attacking entity can become over-represented. To ensure this security property, current epidemic platforms use a Proof-of-Stake system to select peer samples. However such a system limits the openness of the system as only nodes with significant stake can participate in the consensus, leading to an oligopoly situation. Moreover, this design introduces a complex interdependency between the consensus algorithm and the cryptocurrency built upon it. In this paper, we propose a radically different security design for the peer sampling service, based on the distribution of IP addresses to prevent Sybil attacks. We propose a new algorithm, $\scriptstyle{BASALT}$, that implements our design using a stubborn chaotic search to counter attackers' attempts at becoming over-represented. We show in theory and using Monte Carlo simulations that $\scriptstyle{BASALT}$ provides samples which are extremely close to the optimal distribution even in adversarial scenarios such as tentative Eclipse attacks. Live experiments on a production cryptocurrency platform confirm that the samples obtained using $\scriptstyle{BASALT}$ are equitably distributed amongst nodes, allowing for a system which is both open and where no single entity can gain excessive power.
Blockchain-based Distributed Ledgers (DLs) promise to transform the existing financial system by making it truly democratic. In the past decade, blockchain technology has seen many novel applications ranging from the banking industry to real estate. However, in order to be adopted universally, blockchain systems must be scalable to support a high volume of transactions. As we increase the throughput of the DL system, the underlying peer-to-peer network might face multiple levels of challenges to keep up with the requirements. Due to varying network capacities, the slower nodes would be at a relative disadvantage compared to the faster ones, which could negatively impact their revenue. In order to quantify their relative advantage or disadvantage, we introduce two measures of network fairness, $p_f$, the probability of frontrunning and $α_f$, the publishing fairness. We show that as we scale the blockchain, both these measures deteriorate, implying that the slower nodes face a disadvantage at higher throughputs. It results in the faster nodes getting more than their fair share of the reward while the slower nodes (slow in terms of network quality) get less. Thus, fairness and scalability in blockchain systems do not go hand in hand. In a setting with rational miners, lack of fairness causes miners to deviate from the "longest chain rule" or undercut, which would reduce the blockchain's resilience against byzantine adversaries. Hence, fairness is not only a desirable property for a blockchain system but also essential for the security of the blockchain and any scalable blockchain protocol proposed must ensure fairness.
Muhammad Anas Imtiaz, David Starobinski, Ari Trachtenberg
Orphan transactions are those whose parental income sources are missing at the time that they are processed. These transactions typically languish in a local buffer until they are evicted or all their parents are discovered, at which point they may be propagated further. To date, there has been little work in the literature on characterizing the nature and impact of such orphans, and yet it is intuitive that they should affect the performance of the Bitcoin network. This work thus seeks to methodically research such effects through a measurement campaign on live Bitcoin nodes. Our data show that about 45% of orphan transactions end up being included in the blockchain. Surprisingly, orphan transactions tend to have fewer parents on average than non-orphan transactions, and their missing parents have a lower fee, larger size, and lower transaction fee per byte than all other received transactions. Moreover, the network overhead incurred by these orphan transactions can be significant, exceeding 17% when using the default orphan memory pool size (i.e., 100 transactions), although this overhead can be made negligible, without significant computational or memory demands, if the pool size is simply increased to 1000 transactions. Finally, we show that when a node with an empty mempool first joins the network, 25% of the transactions that it receives become orphan, whereas in steady-state this quantity drops to about 1%.