Decentralised ledgers are a prime application case for consensus protocols. Changing sets of validators have to agree on a set of transactions in an asynchronous network and in the presence of Byzantine behaviour. Major research efforts focus on creating consensus protocols under such conditions, with proof-of-stake (PoS) representing a promising candidate. PoS aims to reduce the waste of energy inherent to proof-of-work (PoW) consensus protocols. However, a significant challenge is to get PoS protocols "right", i.e. ensure that they are secure w.r.t. safety and liveness. The "Correct-by-Construction" (CBC) Casper approach by the Ethereum project employs pen-and-paper proofs to ensure its security. CBC Casper is a framework to define consensus protocols and aims to prove safety without loss of abstractness. Each member of the CBC Casper family of protocols is defined by five parameters. CBC Casper models the protocol by a state of each validator and messages sent by validators. Each validator can transition its state using messages by other validators that include their current consensus value and a justification (i.e. their previous messages). We extend CBC Casper in three ways. First, we summarise the research of CBC Casper and extend the definitions of safety and liveness properties. To this end, we discuss an instance of CBC Casper called Casper The Friendly GHOST (TFG), a consensus protocol using a variant of the GHOST fork-choice rule. Second, we refine the properties of messages and states in CBC Casper and give a definition of blockchain safety for Casper TFG. Third, we formally verify the CBC Casper framework together with our refined message and state properties as well as our blockchain safety definition in the Isabelle/HOL proof assistant.
A variety of solutions, e.g., Proof-of-Work (PoW), Proof-of-Stake (PoS), Proof-of-Burn (PoB), and Proof-of-Elapsed-Time (PoET), have been proposed to make consensus mechanism used by the blockchain technology more democratic, efficient, and scalable. However, these solutions have a number of limitations, e.g., PoW approach requires a huge amount of computational power, scales poorly, and wastes a lot of electrical energy. Recently, an innovative protocol called Algorand has been proposed to overcome these limitations. Algorand not only guarantees an overwhelming probability of linearity of the blockchain, but it also aims to solve the âblockchain trilemmaâ of decentralization, scalability, and security. In this paper, we present a security analysis of Algorand. To the best of our knowledge, it is the first security analysis as well as the first formal study on Algorand. We designed an attack scenario in which a group of malicious users tries to break the protocol, or at least limit it to a reduced partition of network users, by exploiting a security flaw in the messages validation process of the Byzantine Agreement (BA). Since the source code or an official simulator for Algorand was not available at the time of our study, we created a simulator (which is available on request) to implement the protocol and assess the feasibility of our attack scenario. Our attack requires the attacker to merely have the trivial capability of establishing multiple connections with targeted nodes, and it costs practically nothing to the attacker. Our results show that it is possible to slow down the message validation process on honest nodes - which eventually forces them to select default values on the consensus - leaving the targeted nodes behind in the chain as compared to the non-attacked nodes. Even though our results are subject to the real implementation of the protocol, the core concept of our attack remains valid.
A blockchain is a distributed ledger forming a distributed consensus on a history of transactions, and is the underlying technology for the Bitcoin cryptocurrency. However, its applications are far beyond the financial sector. The transaction verification process for cryptocurrencies is much slower than traditional digital transaction systems. One approach to increase transaction speed and scalability is to identify a solution that offers faster Proof of Work. In this paper, we propose a method for accelerating the process of Proof of Work based on parallel mining rather than solo mining. The goal is to ensure that no more than two or more miners put the same effort into solving a specific block. The proposed method includes a process for selection of a manager, distribution of work and a reward system. This method has been implemented in a test environment that contains all the characteristics needed to perform Proof of Work for Bitcoin and has been tested, using a variety of case scenarios, by varying the difficulty level and number of validators. Preliminary results show improvement in the scalability of Proof of Work up to 34% compared to the current system.
The lack of interoperability among IoT platforms has led to a fragmented environment, where the users and society as a whole suffer from lock-ins, lack of privacy, and reduced functionality. This paper presents SOFIE, a solution for federating the existing IoT platforms in an open and secure manner using Distributed Ledger Technologies (DLTs) and without requiring modifications to the IoT platforms, and describes how SOFIE is used to enable two complex real life pilots: food supply chain tracking from field to fork and electricity distribution grid balancing with guided electrical vehicle (EV) charging. SOFIE's main contribution is to provide interoperability between IoT systems while also enabling new functionality and business models.
Sharing traffic information on the vehicular network can help in the implementation of intelligent traffic management, such as car accident warnings, road construction notices, and driver route changes to reduce traffic congestion earlier. In the future, in the case of autonomous driving, traffic information will be exchanged more frequently and more immediately. Once the exposed traffic incident is incorrect, the driving route will be misleading, and the driving response may be in danger. The blockchain ensures the correctness of data and tampers resistance in the consensus mechanism, which can solve such similar problems. This paper proposes a proof-of-event consensus concept applicable to vehicular networks rather than proof-of-work or proof-of-authority approaches. The traffic data are collected through the roadside units, and the passing vehicles will verify the correctness when receiving the event notification. In addition, a two-phase transaction on blockchain is introduced to send warning messages in appropriate regions and time periods. The simulation results show that the proposed mechanism can effectively feedback the correctness of traffic events and provide traceable events with trust verification.
A blockchain is a distributed ledger comprised of practically unchange- able, digital recorded data in packages called blocks. Each block in the chain contains data and is cryptographically hashed. The blocks of hashed data draw upon the previous block in the chain, ensuring all data in the overall blockchain is untampered. Blockchain and Distributed Ledger ad- vantages are related to enhanced transparency in business applications and between the involved parties compared to using ordinary databases. Since the blockchain is cryptographically protected, it can be shared, al- lowing anyone to check the correctness of a transaction. Previously, this technology was mostly used for enabling public, decent- ralized digital currencies, known as cryptocurrencies, such as BitCoin and LiteCoin. In the latest years, however, additional use-cases have been de- signed, including non-money asset tokenization, digital identity and sup- ply chain management. Together with the rise of new use-cases, distrib- uted ledger technology frameworks emerged to assist and simplify the development process of such use-cases. These frameworks accelerate the development process at the cost of resource overhead. In this thesis, we use Hyperledger Fabric, a distributed ledger technology framework maintained by the Linux Foundation, to design, develop and analyze the performance of a use-case granted by DNV-GL. We explore the network resource cost of a transaction and model the network traffic flow. In addition, we measure and present the performance of this system and demonstrate why such a performance display alone is misleading.
Jan 1, 2019¡Proceedings of the ... Annual Hawaii International Conference on System Sciences/Proceedings of the Annual Hawaii International Conference on System Sciences
The Internet of Things (IoT) describes the fusion of the physical and digital world which enables assets on the edge to send data to a platform where it gets analyzed. Defined actions are then triggered to influence cross-functional edge activities. Furthermore, on the platform tier functionalities and relations need to be identified and implemented to realize assets operating autonomously and ubiquitously. The exploration of this paper results in the identification of autonomous characteristics and shows functional components to implement autonomous assets on the edge. Distributed Ledger Technology (DLT) and its fusion with Machine Learning (ML) as an area of Artificial Intelligence (AI) provides an integral part to realize the described outline. Thus, the recognition of DLTâs and MLâs usage in the IoT and the evaluation of the relevance as well as the synergies build the main focus of this paper.
Distributed Ledger Technology (DLT) is promising to become the foundation of many decentralised systems. However, the unbalanced and unregulated network layout contributes to the inefficiency of DLT especially in the Internet of Things (IoT) environments, where nodes connect to only a limited number of peers. The data communication speed globally is unbalanced and does not live up to the constraints of efficient real-time distributed systems. In this paper, we introduce a new communication protocol, which enables nodes to calculate the tradeoff between connecting/disconnecting a peer in a completely decentralised manner. The network layout globally is continuously re-balancing and optimising along with nodes adjusting their peers. This communication protocol weakened the inequality of the communication network. The experiment suggests this communication protocol is stable and efficient.
Ghareeb Falazi, Michael Hahn, Uwe Breitenbßcher, Frank Leymann ¡ 5 authors
Blockchains are distributed systems that facilitate the interaction of autonomous entities with limited mutual trust. Many of them support transactional applications known as smart contracts, which access and modify the shared world state. Permissionless blockchains are completely decentralized and do not require mutual trust between interacting peers, but at the expense of having low performance and limited data confidentiality capabilities. On the other hand, permissioned blockchains solve these issues, but sacrifice complete decentralization and involve more trust assumptions. Therefore, there is no single blockchain system suitable for all use-cases. However, this becomes a serious integration challenge for enterprises that need to interact with multiple permissioned and permissionless blockchains in the same context. To facilitate this, we propose an approach that enables composing smart contract functions of various permissioned and permissionless blockchain systems by providing the ability to invoke them directly from business process models using a new task type. To keep this task blockchain-agnostic, we designed a generic technique to identify smart contract functions, as well as a generic metric to describe the degree-of-confidence in the finality of blockchain transactions. Thereby, the proposed approach extends our previous work, BlockME, which provides business modeling extensions only suitable for interacting with permissionless blockchains. To validate the practical feasibility of our approach, we provide a detailed system architecture and a prototypical implementation supporting multiple blockchains.
Derek Leung, Adam Suhl, Yossi Gilad, Nickolai Zeldovich
Decentralized cryptocurrencies rely on participants to keep track of the state of the system in order to verify new transactions. As the number of users and transactions grows, this requirement becomes a significant burden, requiring users to download, verify, and store a large amount of data to participate.
Federico Matteo BenÄiÄ, Alen Hrga, Ivana Podnar Ĺ˝arko
Current consumer grade hardware running a full DLT node takes a long time to synchronize with the network and requires a lot of resources. Nodes that have never before synchronized with the network require significant resources to verify entire ledger history. The initial synchronization assumes inherent trust in the bootstrap nodes, which is a point of centralization. In the case when bootstrap nodes cannot be trusted, a new node might find itself in a malicious cluster of nodes that can either make the node waste resources before realizing that it has been exposed to malicious data, or subvert it into thinking that it has downloaded the longest chain. The Aurora algorithm is able to detect the existence of malicious cliques with a certain plausibility when a new node is attempting to synchronize with the network, and will try to exit cliques identified as malicious. If the node is unable to exit a malicious clique, the node will halt its operation. Furthermore, the same algorithm can be applied to verify if a specific transaction has been included into a referent block with a certain plausibility without the need to download the entire chain (or the header chain), or to trust centralized block explorers. Thus, the Aurora algorithm has the potential to significantly improve the scalability of DLT by reducing the time necessary for initial blockchain synchronization. Furthermore, it strengthens the trustless environment by incentivizing users not willing to run a full or even a light node to partly verify transaction inclusion without relying on third party entities.
Ali Shahaab, B. Lidgey, Chaminda Hewage, Imtiaz Khan
Advancement of consensus protocols in recent years has enabled distributed ledger technologies (DLTs) to find its application and value in sectors beyond cryptocurrencies. Here we reviewed 66 known consensus protocols and classified them into philosophical and architectural categories, also providing a visual representation. As a case study, we focus on the public sector and highlighted potential protocols. We have also listed these protocols against basic features and sector preference in a tabular format to facilitate selection. We argue that no protocol is a silver bullet, therefore should be selected carefully, considering the sector requirements and environment.
Marianna Belotti, Nikola Bozic, Guy Pujolle, Stefano Secci
Blockchain is a technology making the shared registry concept from distributed systems a reality for a number of application domains, from the cryptocurrency one to potentially any industrial system requiring decentralized, robust, trusted, and automated decision making in a multi-stakeholder situation. Nevertheless, the actual advantages in using blockchain instead of any other traditional solution (such as centralized databases) are not completely understood to date, or at least there is a strong need for a vademecum guiding designers toward the right decision about when to adopt blockchain or not, which kind of blockchain better meets use-case requirements, and how to use it. In this paper, we aim at providing the community with such a vademecum, while giving a general presentation of blockchain that goes beyond its usage in Bitcoin and surveying a selection of the vast literature that emerged in the last few years. We draw the key requirements and their evolution when passing from permissionless to permissioned blockchains, presenting the differences between proposed and experimented consensus mechanisms, and describing existing blockchain platforms.
In this paper, we present the most extensive evaluation of blockchain system to date. To achieve scalability across servers in more than 10 countries located on 4 different continents, we drastically revisited Byzantine fault tolerant blockchains and verification of signatures. The resulting blockchain, called the Red Belly Blockchain (RBBC), commits more than a hundred thousand transactions issued by permissionless nodes. These transactions are grouped into blocks within few seconds through a partially synchronous consensus run by permissioned nodes. It prevents double spending by guaranteeing that a unique block is decided at any given index of the chain in a deterministic way by all participants. We compared the performance of RBBC against traditional Byzantine fault tolerant alternatives and more recent randomized solutions. In the same geo-distributed environment with low-end machines, we noticed two interesting comparisons: (i) the RBBC throughput scales to hundreds of machines whereas the classic 3-step leader-based BFT state machine used by consortium blockchains cannot scale to 40 identically configured nodes; (ii) RBBC guarantees transaction finality in 3 seconds and experiences a third of the latency that randomized-based solutions like HoneyBadgerBFT can offer. This empirical evaluation demonstrates that blockchain scalability can be achieved without sacrificing security.