The blockchain technology introduced in Satoshi Nakamoto's paper "Bitcoin: A Peer-to-Peer Electronic Cash System" bring a realistic distributed way of transaction to this world. The alternative blockchain Ethereum improved some demerits of Bitcoin. However, the major problem still exists - hash-based proof-of-work requires heavy computing power and hurts the scalability. In this paper, we propose a lightweight blockchain called ZeroCalo. It constructs thousands of miner nodes into DHT (Distributed Hash Table) structure. Efficient message broadcast and key lookup are developed. With them, a consensus-based proof-of-work algorithm for distributed ledger is fulfilled. The evaluation shows that a transaction requires O(logN) of time and O(N) of bandwidth consumption. ZeroCalo consumes very little energy while providing good TPS. This property makes it possible to be deployed on IOT device network or low-end hosts in cloud environment.
Consensus mechanism is the heart of any blockchain network. Many projects have proposed alternative protocols to improve restricted scalability of Proof of Work originated since Bitcoin. As an improvement of Delegated Proof of Stake, in this paper, we introduce a novel consensus, namely, Delegated Proof of Reputation, which is scalable, secure with an acceptable decentralization. Our innovative idea is replacing pure coinstaking by a reputation ranking system essentially based on ranking theories (PageRank, NCDawareRank and HodgeRank).
Vero Estrada-Galiñanes, Racin Nygaard, Viktor Trón, Rodrigo Q. Saramago · 6 authors
Blockchain is the driving force behind a myriad of decentralized applications (dapps) that promise to transform the Internet. The next generation Internet, or web3, introduces a "universal state layer" to store data in p2p networks. Swarm, a native layer of the Ethereum web3 stack, aims at providing redundant storage for dapp code, data, as well as, blockchain and state data. Based on a diploma verification dapp use case, we share insights on the role of redundancy strategies in designing a reliable storage layer. Our proof-of-concept improves Swarm's resilience to failures by balancing repairs and storage, with a slightly added latency.
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.
This paper proposes a decentralized solution for web hosting based on interplanetary file system (IPFS) and Ethereum blockchain. Particularly, we use Ethereum smart contracts to manage the IPFS network and the web hosting service. IPFS platform is used to store data and to host websites. All storage miner nodes on the IPFS network offer the pinning service to ensure that source codes of the websites and users' data are retained long-term. Moreover, these nodes also enable the interplanetary name space (IPNS) service for creating and updating mutable links to IPFS contents. TXT record is also used in the domain name system (DNS) to map domain names to IPNS addresses for hosted websites. For privacy-preserving data storage, websites need to be deployed an encryption algorithm. The proposed model that combines between the IPFS and blockchain networks to form a platform providing the decentralized web hosting service. Experiment illustrates building and hosting a web application on the IPFS network. Experimental results show that, compared to the traditional web hosting model, the hosted web application on the proposed platform ensures the confidentiality, integrity, and availability.
Blockchain is a distributed ledger, characterized by immutability, anonymity and auditability without requiring trust third party. To provide data exchanges to form such ledger, blockchain network enables the dissemination of transactions and blocks to reach the consensus, which mainly consists of attachment strategy and communication strategy. Currently, it is implemented with peer-to-peer overlay network, which, however, suffers from the intrinsic problem of mismatching between traffic flows and underlying network topology. To solve this problem, we employ information-centric networking (ICN) approach to design a decentralized information-centric blockchain network (DIBN), where categories are named to enable the traffic to be decentralized and an any-to-all category dissemination structure (CDS) is established among all the blockchain nodes (BNs) for each category. For the CDS, one BN can efficiently send data to all other BNs aligning the traffic with the underlying network, which overcomes the problem of mismatch. The performance analysis shows that the proposed DIBN can greatly reduce the average path length for data dissemination in blockchain.
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.
Online publishing of news and information enables important content to reach a much larger audience than traditional paper publishing, but there is no guarantee of long-term, reliable, and persistent access to the content. Over time, links "decay" because they are not reliably updated when content changes location, or even worse, content is deliberately altered from its original published form or deleted altogether. We present the design of Watchdog, a permissioned distributed ledger that securely and reliably monitors and preserves dynamic web content such as government and news sites. Unlike prior preservation systems, our system design allows nodes to be dispersed across multiple administrative domains, thus eliminating single points of trust and at the same time, is the first to monitor how content changes both over time and across geographical location. Watchdog achieves Byzantine fault-tolerance via a novel interactive consistency algorithm that offers a twist on the traditional definition and use of interactive consistency; the algorithm enables a set of mutually suspicious nodes, with arbitrary-sized, potentially overlapping data collections, to efficiently agree on the exact data collection in possession by each node. We demonstrate how our algorithm enables Watchdog nodes to exchange and agree upon the content each has observed individually, in a fault-tolerant, tamper-proof manner.
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.
Cryptocurrencies are digital assets which depend upon the use of distributed peer-to-peer networks. The method a new peer uses to initially join a peer-to-peer network is known as bootstrapping. The ability to bootstrap without the use of a centralized resource is an unresolved challenge. In this paper we survey the bootstrapping techniques used by 74 cryptocurrencies and find that censorship-prone methods such as DNS seeding and IP hard-coding are the most prevalent. In response to this finding, we test two other bootstrapping techniques less susceptible to censorship, Tor and ZMap, to determine if they are operationally feasible alternatives more resilient to censorship. We perform a global measurement study of DNS query responses for each the 92 DNS seeds discovered across 42 countries using the distributed RIPE Atlas network. This provides details of each cryptocurrencies' peer-to-peer network topology and also highlights instances of DNS outages and query manipulation impacting the bootstrapping process. Our study also reveals that the source code of the cryptocurrencies researched comes from only five main repositories; hence accounting for the inheritance of legacy bootstrapping methods. Finally, we discuss the implications of our findings and provide recommendations to mitigate the risks exposed.
Bitcoin is a top-ranked cryptocurrency that has experienced huge growth and survived numerous attacks. The protocols making up Bitcoin must therefore accommodate the growth of the network and ensure security.
The pervasiveness of IoT devices makes the delivery mechanism of security updates a challenge. Current IoT systems rely on centralized or brokered paradigms or clouds with huge computational and storage capacities. The existing centralized IoT setups are therefore expensive as the result of factors such as the high costs associated with cloud server and network infrastructures and maintenance. Thus, the need for a fully decentralized peer to peer and secure technology to overcome these problems rises into the realm of existence. Blockchain provides a solution that fulfills the requirements of such a platform. Ideally, the update infrastructure should implement the CIA triad properties (Confidentiality, Integrity, and Availability). In this article, we study how a blockchain application can meet these requirements and propose a novel system to decentrally distribute digital content in a peer-to-peer network using the blockchain technology and smart contracts to overcome the concerns mentioned above. Additionally, in order to prevent the issues stemming from the free-riding challenge in P2P networks (peers refrain to generously share their resources to distribute updates), we exploit a Nash equilibrium micropayment mechanism to grant adequate incentive for peers to participate in distributing IoT update files.
Abstract We have implemented a blockchain system based on Ethereum for use by a university to store student grades and to provide a cryptocurrency. Based upon an exploratory, qualitative evaluation we have found several tensions between the concept of a university as an organization and the concept of distributed autonomous organizations (DAOs) in Ethereum. These include tensions in (i) mechanisms of trust, (ii) boundaries of openness and (iii) values in procedures. In this article we outline our implementation and the evaluation process.
Aicha Fatrah, Said El Kafhali, Abdelkrim Haqiq, Khaled Salah
Blockchain is becoming the missing puzzle to solve many digital services problems these days. In this paper, we propose a design and implementation of a Blockchain-based voting system that can be used in national elections. In the paper, we argue that our Blockchain-based voting system is more secure, reliable and it has the ability to protect voter privacy which will help boost the number of voters and their trust in the electoral system as well as reducing considerably the cost of national elections.
With the popularity of artificial intelligence(AI), intelligent agents are potential to positively change people's lives in every aspect. Meanwhile, blockchain technology opens a new era of value exchange with trustless security among strangers. Its decentralized architecture and cryptography based data storage pattern bring light to vast application areas with high security and scalability requirements. In this work, we provide a general solution for intelligence application development on blockchain. Specifically, we propose a novel design of a smart agent inspired by the smart contract concept in the blockchain. Based on the proposed smart agents, a system architecture composed by smart agents is built supported by blockchain, where the agent network and blockchain network is overlapped. Then, a demonstration of the proposed architecture is designed in a case where private data required to be "properly protected" in a distributed manner. The implementation of the designed system is further conducted in the Ethereum development environment, showing the effectiveness and applicability of the proposed architecture in developing a secure distributed application.
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-Cossío
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.
In blockchain, delivering block data, especially delivering all historical blocks to a new node, will cost lots of bandwidth consumption. This cost may dissuade nodes from sharing their blocks to new or rejoined peer. In this paper, we present some incentive schemes for this kind of data sharing behaviour. In our design, node participating in delivering their storage data to their peers can get some rewards from the node who request the data. We adopt coin-locking strategy to discourage dishonest behaviour in the sharing process. Nodes need not put a large deposit to big data sharing since the data sharing process can be divided into smaller ones, and micropayment channel is set to accelerate the speed of during each small transmitting process. We give a theoretical analysis of our mechanism and discuss its practical application of data sharing in some mainstream cryptocurrencies and blockchains in IoT industry.
With the continuous development of blockchain technology, more and more blockchain projects use semi-distributed P2P network structures. Although original gossip algorithm can be devoted to data synchronization in semi-distributed blockchain network, it can not be well applied to actual network environment. Since the probability of selecting a target node during data synchronization is fixed, it is inevitable that a message can be sent to a duplicate node. It will not only cause a lot of redundant messages, but also bring inefficient data synchronization. To address this problem, this paper proposes an improved HNA-Gossip algorithm which can reduce the probability of selecting duplicate nodes to send messages by recording historical node information dynamically. The simulation results show that, compared with the original gossip algorithm, various aspects of HNA-Gossip algorithm perform better.
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.