We propose BlockLot, a blockchain based verifiable lottery. BlockLot provides transparent, immutable, fair, and verifiable lottery services enhanced by recent blockchain technologies such as append-only (replicated) distributed ledger and smart contract. In addition, BlockLot allows all participants to perform various verification to ensure that the system is actually working as expected. We implement BlockLot services which includes open, query, subscribe, and draw in smart contracts. We also develop webbased user interface for using the lottery services provided by BlockLot. The web interface allows the user to verify the lottery as well.
The success and popularity of Bitcoin mainly focuses the underlying blockchain technology which is totally immutable distributed ledger, highly secured by its P2P network consensus named Proof of Work (PoW). One of the worst threats to a Proof-of-Work based cryptocurrency is 51% attack. If one or more dishonest network peer gains more than 50% of resource such as processing power, then they will become the majority decision maker in the network. It is already proved that mixing of two or more existing protocol that is called hybrid protocol can make the network enough resistive to this attack. The recent implementations of hybrid protocols have other limitations and problems that they are facing and striving to resolve. But their main weakness is in distribution of block mining reward to the investors. From the perspective of an investor, an investor invests his hard-earned money in a cryptocurrency for making proper profit from his investment. The main source of this profit is the block reward which is generated and given to the miner on successful mining of a block. So, to ensure this profit is given to proper user on proper time interval, the consistency of block generation time interval is a vital factor. The voting system, ticket system etc. are not time controlled and over all block reward generation interval will not show a uniform distribution of profit. Another big issue is diversifying the peers by creating special committee and groups of validators the concept of P2P network is violated. In this paper we will describe a step by step process to implement a Hybrid PoW-PoS based consensus protocol. In our proposed system, the PoW mining process is only used to regulate the block generation time. The actual block generation is done by the same user with PoS consensus mechanism. There is no voting or validating committee. The entire network will validate each block. This is the major difference with other discussed system. The system will not only be able to tackle the 51% attack, it provides a uniform distribution of mining reward to the stake holders and investors by maintaining a precise block generation interval with difficulty adjustment in PoW mining and probability calculation for stake holders according to their matured staking balance. We will not only show how to make the system non-vulnerable to this attack but also describe in detail about how to validate the transactions and blocks in different stage of creating the block chain.
Proof of Stake (PoS) is a burgeoning Sybil resistance mechanism that aims to have a digital asset ("token") serve as security collateral in crypto networks. However, PoS has so far eluded a comprehensive threat model that encompasses both Byzantine attacks from distributed systems and financial attacks that arise from the dual usage of the token as a means of payment and a Sybil resistance mechanism. In particular, the existence of derivatives markets makes malicious coordination among validators easier to execute than in Proof of Work systems. We demonstrate that it is also possible for on-chain lending smart contracts to cannibalize network security in PoS systems. When the yield provided by these contracts is more attractive than the inflation rate provided from staking, stakers will tend to remove their staked tokens and lend them out, thus reducing network security. In this paper, we provide a simple stochastic model that describes how rational validators with varying risk preferences react to changes in staking and lending returns. For a particular configuration of this model, we provide a formal proof of a phase transition between equilibria in which tokens are predominantly staked and those in which they are predominantly lent. We further validate this emergent adversarial behavior (e.g. reduced staked token supply) with agent-based simulations that sample transitions under more realistic conditions. Our results illustrate that rational, non-adversarial actors can dramatically reduce PoS network security if block rewards are not calibrated appropriately above the expected yields of on-chain lending.
The problem of peer selection, which randomly selects a peer from a set, is commonplace in Proof-of-Stake (PoS) protocols. In PoS, peers are chosen randomly with probability proportional to the amount of stake that they possess. This paper presents an approach that relates PoS peer selection to Roulette-wheel selection, which is frequently used in genetic and evolutionary algorithms or complex network modelling. In particular, we introduce the use of stochastic acceptance algorithm [6] for fast peer selection. The roulette-wheel selection algorithm [6] achieves O(1) complexity based on stochastic acceptance, whereas searching based algorithms may take O(N ) or O(logN ) complexity in a network of N peers.
Modern Blockchains support the execution of user programs, called smart contracts. As a trusted computing platform, smart contracts bring decentralization, computation integrity, open access and information transparency to average users on the Internet. However, running smart-contract programs leads to high costs, known as Gas. Such costs prevent the use of smart contracts in data-intensive application scenarios, such as high-frequency trading and transparency logging. This paper addresses the Gas-based cost effectiveness in the most consuming layer of a smart contract, namely data storage. We present GRuB, a dynamic data-replication framework that monitors the smart-contract workload and makes online replication decisions. A new online algorithm is proposed that provides constant-bounded 'competitiveness' in Gas. To further save Gas, the workload monitor and decision maker are run off the Blockchain and with security against the forging of workload trace being monitored. A GRuB prototype is built, including a smart-contract component on Ethereum and an off-chain middleware on top of Google LevelDB. The cost evaluation under the YCSB workloads shows that GRuB can converge quickly to changing workloads and save Gas significantly compared with static replication schemes. Two case studies are conducted for data-intensive applications, including high-frequency trading and transparency logging, in which running GRuB leads to affordable Gas.
Blockchain platforms like Bitcoin and Ethereum have introduced a distributed and decentralized cryptocurrency system with no third-party intermediation required. These peer to peer network systems allows Internet users to directly transact with each other. However due to the heavy emphasis on decentralization, scalability has taken a back seat. It has also become a key issue in the wider adoption of these technologies. The change to the underlying data organizing structure to Direct Acyclic Graphs (DAG) of the distributed ledger, has significantly increased transaction scalability. In this paper, we analyse some of the Distributed Ledger Technologies that use DAGs and have shown marked improved in transaction performance without weakening security.
Georgios Birmpas, Ηλίας Κουτσουπιάς, Philip Lazos, Francisco J. Marmolejo-CossÃo
Bitcoin is a decentralised digital currency that serves as an alternative to existing transaction systems based on an external central authority for security. Although Bitcoin has many desirable properties, one of its fundamental shortcomings is its inability to process transactions at high rates. To address this challenge, many subsequent protocols either modify the rules of block acceptance (longest chain rule) and reward, or alter the graphical structure of the public ledger from a tree to a directed acyclic graph (DAG). Motivated by these approaches, we introduce a new general framework that captures ledger growth for a large class of DAG-based implementations. With this in hand, and by assuming honest miner behaviour, we (experimentally) explore how different DAG-based protocols perform in terms of fairness, i.e., if the block reward of a miner is proportional to their hash power, as well as efficiency, i.e. what proportion of user transactions a ledger deems valid after a certain length of time. Our results demonstrate fundamental structural limits on how well DAG-based ledger protocols cope with a high transaction load. More specifically, we show that even in a scenario where every miner on the system is honest in terms of when they publish blocks, what they point to, and what transactions each block contains, fairness and efficiency of the ledger can break down at specific hash rates if miners have differing levels of connectivity to the P2P network sustaining the protocol.
We design and implement Publication Chain (PubChain), a decentralized open-access publication platform built on decentralized and distributed technologies of blockchain and IPFS peer-to-peer file sharing systems. The existing publication platforms have some severe drawbacks. First, instead of promoting widespread knowledge sharing, access to publications on the platforms owned by publishers is often on a fee basis. This drawback of pay wall prevents researchers from "standing on the shoulders of giants". Moreover, the peer review process on most all existing publication platforms (including both open-access and publisher platforms) is prone to be ineffective, since there is no proper incentive to reviewers for performing high-qualified reviews. PubChain is an alternative platform to the existing publication venues aiming to address their drawbacks. No central third-party owns the contents (i.e., papers and reviews) of PubChain. Exploiting blockchain technology, we devise an elaborate incentive scheme on PubChain to incentivize key stakeholders (i.e., authors, readers and reviewers) to participate publication activities on PubChain in a substantive manner by earning credits and rewards through self-motivated interactions. We have performed simulations to investigate the robustness of our proposed incentive scheme against fraudulent publications and reviews. We also have implemented a prototype of PubChain to demonstrate its key concepts.
Denis Rangelov, Nikolay Tcholtchev, Philipp Lämmel, Ina Schieferdecker
In recent years the emergence of the Ethereum Blockchain has introduced a new alternative perspective on how web applications can be build. More precisely, the Ethereum Blockchain allows the development of applications, where programming code can be executed in a decentralized manner with no restrictions imposed by a central authority. However, as it is the case with many emerging technologies, there is a fair amount of trade-offs that have to be considered when this technology is used as a platform for implementing decentralized applications. In this work we present two architectural designs for building decentralized applications (DApps) based on the Ethereum Blockchain technology. Within this context, we discuss the inherent strengths and weaknesses of each of the architectural designs as well as the set of challenges that we faced during the development process.
Matteo Varvello, Iñigo Querejeta Azurmendi, Antonio Nappa, Panagiotis N. Papadopoulos · 6 authors
Distributed Virtual Private Networks (dVPNs) are new VPN solutions aiming to solve the trust-privacy concern of a VPN's central authority by leveraging a distributed architecture. In this paper, we first review the existing dVPN ecosystem and debate on its privacy requirements. Then, we present VPN0, a dVPN with strong privacy guarantees and minimal performance impact on its users. VPN0 guarantees that a dVPN node only carries traffic it has "whitelisted", without revealing its whitelist or knowing the traffic it tunnels. This is achieved via three main innovations. First, an attestation mechanism which leverages TLS to certify a user visit to a specific domain. Second, a zero knowledge proof to certify that some incoming traffic is authorized, e.g., falls in a node's whitelist, without disclosing the target domain. Third, a dynamic chain of VPN tunnels to both increase privacy and guarantee service continuation while traffic certification is in place. The paper demonstrates VPN0 functioning when integrated with several production systems, namely BitTorrent DHT and ProtonVPN.
A blockchain is a database of sequential events that is maintained by a distributed group of nodes. A key consensus problem in blockchains is that of determining the next block (data element) in the sequence. Many blockchains address this by electing a new node to propose each new block. The new block is (typically) appended to the tip of the proposer's local blockchain, and subsequently broadcast to the rest of the network. Without network delay (or adversarial behavior), this procedure would give a perfect chain, since each proposer would have the same view of the blockchain. A major challenge in practice is forking. Due to network delays, a proposer may not yet have the most recent block, and may, therefore, create a side chain that branches from the middle of the main chain. Forking reduces throughput, since only one a single main chain can survive, and all other blocks are discarded. We propose a new P2P protocol for blockchains called Barracuda, in which each proposer, prior to proposing a block, polls $\ell$ other nodes for their local blocktree information. Under a stochastic network model, we prove that this lightweight primitive improves throughput as if the entire network were a factor of $\ell$ faster. We provide guidelines on how to implement Barracuda in practice, guaranteeing robustness against several real-world factors.
Off-chain transaction networks can mitigate the scalability issues of today's trustless electronic cash systems such as Bitcoin. However, these peer-to-peer networks also introduce a new attack surface which is not well-understood today. This paper identifies and analyzes, a novel Denial-of-Service attack which is based on route hijacking, i.e., which exploits the way transactions are routed and executed along the created channels of the network. This attack is conceptually interesting as even a limited attacker that manipulates the topology through the creation of new channels can navigate tradeoffs related to the way it attacks the network. Furthermore, the attack also highlights a fundamental design tradeoff for the defender (who determines its own routes): to become less predictable and hence secure, a rational node has to pay higher fees to nodes that forward its payments. We find that the three most common implementations for payment channels in Bitcoin (lnd, C-lightning, Eclair) approach routing differently. We begin by surveying the current state of the Lightning network and explore the routes chosen by these implementations. We find that in the current network nearly 60\% of all routes pass through only five nodes, while 80\% go through only 10 nodes. Thus, a relatively small number of colluding nodes can deny service to a large fraction of the network. We then turn to study an external attacker who creates links to the network and draws more routes through its nodes by asking for lower fees. We find that just five new links are enough to draw the majority (65\% - 75\%) of the traffic regardless of the implementation being used. The cost of creating these links is very low. We discuss the differences between implementations and eventually derive our own suggested routing policy, which is based on a novel combination of existing approaches.
James Kempf, Sambit Nayak, Remi Robert, Jim Feng · 9 authors
In this paper, we describe a virtual services marketplace, called Nubo, designed to connect buyers of virtual services (or tenants) with providers of those services on a cloud computing platform. The marketplace is implemented as a collection of distributed microservices along with a marketplace portal that runs as a Web application. The heart of Nubo is the Saranyu tenant and service management microservice. Saranyu is a decentralized application (dApp) built on top of the J.P. Morgan Quorum blockchain. Tenant and service accounts are represented as static (nonnegotiable) smart contracts written in the Solidity language. Quorum provides a tamper evident and tamper resistant distributed ledger, whereby multiple cloud and service providers can co-operate to provide service resources to tenants in a trustworthy fashion. Services offer resources consisting of a collection of attributes describing what the tenant can consume, and tenants subscribe to service resources through the Nubo Marketplace portal. The Service Manager microservice provides multitenant support for containerized services built for deployment and orchestration using Docker that were originally not designed to be managed through Saranyu. We discuss our design goals for Nubo, describe the overall architecture, discuss some details on how Saranyu uses the blockchain and smart contracts, and provide comprehensive performance and scalability data measured on the Saranyu REST API. The results indicate Saranyu is competitive with published results for comparable operations on the Havana release of OpenStack Keystone, but Saranyu provides a much richer collection of tenant and service management functionality than Keystone.
Iago Sestrem Ochôa, Rafael Alexandre Piemontez, Lucas M. C. e Martins, Valderi Reis Quietinho Leithardt · 5 authors
Blockchain technology has aroused the interest of researchers as it ensures security and privacy in decentralized applications. One of the platforms currently used for the development of new blockchain-based solutions is the Ethereum network. This article presents an experimental analysis of the scalability of this network to identify its cost and performance for several contracts in a simulated private Ethereum network. The results obtained demonstrate that storage operations for large amounts of data can prevent the use of blockchain due to the high cost of gas charged for this type of operation. The experiments also pointed out that processing operations which do not store information have a small cost of gas.
In the highly connected age of information and data, the push for the development of ‘clean data’ has necessitated sustainability strategies for data centers. Green innovations are increasingly implemented to reduce the formidable power consumption of inefficient computing processes while heat reuse solutions repurpose the large volumes of server waste heat, decreasing facility footprint. This project examined the efficiency optimization potential of co-located power generation and greenhouse waste heat reuse for cryptocurrency data center platforms in Alberta. The proposed 45 MW data center capitalized on favorable climatic conditions to reduce energy requirements, improving facility efficiency and decreasing theoretical PUE values from 2.13 to 1.51. Resultant waste heat sufficiently supplied year-round heating to an 8.34-acre greenhouse suitable for commercial cannabis growth. The total annual avoided emissions for this proposed system were calculated at 70,000 tonnes of CO2, illustrating the potential of integrated economizer cyles and waste heat reuse in Alberta.
IOTA opened recently a new line of research in distributed ledgers area by targeting algorithms that ensure a high throughput for the transactions generated in IoT systems. Transactions are continuously appended to an acyclic structure called tangle and each new transaction selects as parents two existing transactions (called tips) that it approves. G-IOTA, a very recent improvement of IOTA, targets to protect tips left behind offering hence a good confidence level. However, this improvement had a cost: the use of an additional tip selection mechanism which may be critical in IoT systems since it needs additional energy consumption. In this paper we propose a new metamorphic algorithm for tip selection that offers the best guaranties of both IOTA and G-IOTA. Our contribution is two fold. First, we propose a parameterized algorithm, E-IOTA, for tip selection which targets to reduce the number of random walks executed in previous versions (IOTA and G-IOTA) while maintaining the same security guaranties as IOTA and the same confidence level and fairness with respect to tips selection as G-IOTA. Then we propose a formal analysis of the security guaranties offered by E-IOTA against various attacks mentioned in the original IOTA proposal (e.g. large weight attack, parasite chain attack and splitting attack). Interestingly, to the best of our knowledge this is the first formal analysis of the security guaranties of IOTA and its derivatives.
Tezos is an innovative blockchain that improves on several aspects compared to more established blockchains. It offers an original proof-of-stake consensus algorithm and can be used as a decentralized smart contract platform. It has the capacity to amend its own economic protocol through a voting mechanism and focuses on formal methods to improve safety.
The Sybil attack plagues all peer-to-peer systems, and modern open distributed ledgers employ a number of tactics to prevent it from proof of work, or other resources such as space, stake or memory, to traditional admission control in permissioned settings. With SybilQuorum we propose an alternative approach to securing an open distributed ledger against Sybil attacks, and ensuring consensus amongst honest participants, leveraging social network based Sybil defences. We show how nodes expressing their trust relationships through the ledger can bootstrap and operate a value system, and general transaction system, and how Sybil attacks are thwarted. We empirically evaluate our system as a secure Federated Byzantine Agreement System, and extend the theory of those systems to do so.
Personalized quality of service (QoS) prediction plays an important role in helping users build high-quality service-oriented systems. To obtain accurate prediction results, many approaches have been investigated in recent years. However, these approaches do not fully address untrustworthy QoS values submitted by unreliable users, leading to inaccurate predictions. To address this issue, inspired by blockchain with distributed ledger technology, distributed consensus mechanisms, encryption algorithms, etc., we propose a personalized QoS prediction method for web services that we call blockchain-based matrix factorization (BMF). We develop a user verification approach based on homomorphic hash, and use the Byzantine agreement to remove unreliable users. Then, matrix factorization is employed to improve the accuracy of predictions and we evaluate the proposed BMF on a real-world web services dataset. Experimental results show that the proposed method significantly outperforms existing approaches, making it much more effective than traditional techniques.
With the support of the blockchain systems, the cryptocurrency has changed the world of virtual assets. Digital games, especially those with massive multi-player scenarios, will be significantly impacted by this novel technology. However, there are insufficient academic studies on this topic. In this work, we filled the blank by surveying the state-of-the-art blockchain games. We discuss the blockchain integration for games and then categorize existing blockchain games from the aspects of their genres and technical platforms. Moreover, by analyzing the industrial trend with a statistical approach, we envision the future of blockchain games from technological and commercial perspectives.
Swagatika Sahoo, Akshay M. Fajge, Raju Halder, Agostino Cortesi
In the nine years since its launch, amid intense research, scalability is always a serious concern in blockchain, especially in case of large-scale network generating huge number of transaction-records. In this paper, we propose a hierarchical blockchain model characterized by: (1) each level maintains multiple local blockchain networks, (2) each local blockchain records local transactional activities, and (3) partial views (tunable w.r.t. precision) of different subsets of local blockchain-records are maintained in the blockchains at next level of the hierarchy. To meet this objective, we apply abstractions on a set of transaction-records in a regular time interval by following the Abstract Interpretation framework, which provides a tunable precision in various abstract domain and guarantees the soundness of the system. While this model suitably fits to the real-worlds organizational structures, the proposal is powerful enough to scale when large number of nodes participate in a network resulting into an enormous growth of the network-size and the number of transaction-records. We discuss experimental results on a small-scale network with three sub networks at lower-level and by abstracting the transaction-records in the abstract domain of intervals. The results are encouraging and clearly indicate the effectiveness of this approach to control exponential growth of blockchain size w.r.t. the total number of participants in the network.
This paper proposes an architecture for dynamic decentralized marketplace for trading of Internet of Things data. To this end, we introduce a 3-tier framework which consists of provider, consumer and broker. The framework is realized using multiple trustless broker which matches and selects potential data provider based on the consumers requirements. Rather than using a centralized server to manage the contract between provider and consumer, the framework leverages smart contract-based agreement for automatically enforcing the terms of the contract to the involved parties.
Niclas Kannengießer, Sebastian Lins, Tobias Dehling, Ali Sunyaev
When developing peer-to-peer applications on distributed ledger technology (DLT), a crucial decision is the selection of a suitable DLT design (e.g., Ethereum), because it is hard to change the underlying DLT design post hoc. To facilitate the selection of suitable DLT designs, we review DLT characteristics and identify trade-offs between them. Furthermore, we assess how DLT designs account for these trade-offs and we develop archetypes for DLT designs that cater to specific requirements of applications on DLT. The main purpose of our article is to introduce scientific and practical audiences to the intricacies of DLT designs and to support development of viable applications on DLT.
Blockchains have attracted a great deal of attention as a technology for the distributed management of register information at multiple nodes without a centralized system. However, they possess the drawbacks of low transaction throughput and long approval time. These problems can be addressed by shortening the block generation interval; however, shortening this interval alone has the effect of increasing the frequency of forks. In this study, we aim to shorten the block generation interval without increasing the fork generation rate by improving the network topology of the nodes and shortening the propagation time. We propose a neighbor node selection method forming a network topology with a short block propagation time. A blockchain simulator is used to demonstrate the effect of the proposed neighbor node selection method on the propagation delay of the network. This result indicates that the proposed method improves block propagation time.