Biblio

With the explosive growth of the internet of things (IoT) devices, there are amount of data requirements and computing tasks. Fog computing network that could provide computing, caching and communication resources closer to IoT devices (ID) is considered as a potential solution to deal with the vast computing tasks. To improve the performance of the fog computing network while ensuring data security, blockchain technology is enabled and a location-based reliable sharding (LRS) algorithm is proposed, which jointly considers the optimal number of shards, the geographical location of fog nodes (FNs), and the number of nodes in each shard. Firstly, the reliable sharding result is based on the reputation values of FNs, which are related to the decision information and historical reputation value of FNs in the consensus process. Moreover, a reputation based PBFT consensus algorithm is adopted to accelerate the consensus process. Furthermore, the normalized entropy is used to estimate the proportion of malicious nodes and optimize the number of shards. Finally, simulation results show the effectiveness of the proposed scheme.

FastChain is a simulator built in NS-3 which simulates the networked battlefield scenario with military applications, connecting tankers, soldiers and drones to form Internet-of-Battlefield-Things (IoBT). Computing, storage and communication resources in IoBT are limited during certain situations in IoBT. Under these circumstances, these resources should be carefully combined to handle the task to accomplish the mission. FastChain simulator uses Sharding approach to provide an efficient solution to combine resources of IoBT devices by identifying the correct and the best set of IoBT devices for a given scenario. Then, the set of IoBT devices for a given scenario collaborate together for sharding enabled Blockchain technology. Interested researchers, policy makers and developers can download and use the FastChain simulator to design, develop and evaluate blockchain enabled IoBT scenarios that helps make robust and trustworthy informed decisions in mission-critical IoBT environment.

As a decentralized ledger technology, blockchain is considered to be a potential solution for applications with highly concentrated management mechanism. However, most of the existing blockchain networks are employed with the hash-puzzle-solving consensus protocol, known as proof-of-work. The competition of solving the puzzle introduces high latency, which directly leads to a long transaction-processing time. One solution of this dilemma is to establish a blockchain network with shards. In this paper, we focus on the blockchain network with shards and adopt the security-deposit based consensus protocol, studying the problem of how to balance the security incentive and the economic incentive. Also, the inherent features of the blockchain, i.e., anonymity and decentralization, introduce the information asymmetric issue between the beacon chain and the participants. The contract theory is utilized to formulate the problem between them. As such, the optimal rewards related to the different types of validators can be obtained, as well as the reasonable deposits accordingly. Compared with the fixed deposits, the flexible deposits can provide enough economic incentive for the participants without losing the security incentives. Besides, the simulation results demonstrate that the contract theory approach is capable of maximizing the beacon chain's utility and satisfying the incentive compatibility and individual rationality of the participants.

With features such as decentralization, consistency, tamper resistance, non-repudiation, and pseudonym, blockchain technology has the potential to strengthen the Internet of Things (IoT) significantly, thus opening an intriguing research area in the integration of blockchain and IoT. However, most existing blockchain schemes were not dedicated to the IoT ecosystem and hence could not meet the specific requirements of IoT. This paper aims to fix the gap. Inspired by Chainspace, a blockchain platform which could be applicable in IoT, VChain is proposed, a novel blockchain scheme suitable for IoT which is more secure, concrete, and practical compared with Chainspace. Specifically, in VChain, a two-layer BFT-based consensus protocol with HoneyBadger BFT protocol is proposed and a collective signature scheme as building blocks. The designs above allow for supporting faulty-shards-tolerance and asynchronous network model, which could not be sustained in Chainspace, and keeping high efficiency as well. Moreover, the sharding strategy presented in VChain, different from that in RapidChain, which adopts the energy-consuming PoW mechanism for sharding, is environmentfriendly and thus makes VChain fit for IoT well. Last but not least, VChain also inherits the merits of Chainspace to separate the execution and verification of smart contracts for privacy.

The success and growing popularity of blockchain technology has lead to a significant increase in load on popular permissionless blockchains such as Ethereum. With the current design, these blockchain systems do not scale with additional nodes since every node executes every transaction. Further efforts are therefore necessary to develop scalable permissionless blockchain systems. In this paper, we provide an aggregated overview of the current research on the Ethereum blockchain towards solving the scalability challenge. We focus on the concept of sharding, which aims to break the restriction of every participant being required to execute every transaction and store the entire state. This concept however introduces new complexities in the form of stateless clients, which leads to a new challenge: how to guarantee that critical data is published and stays available for as long as it is relevant. We present an approach towards solving the data availability problem (DAP) that leverages synergy effects by reusing the validators from Casper. We then propose two distinct approaches for reliable collation proposal, state transition, and state verification in shard chains. One approach is based on verification by committees of Casper validators that execute transactions in proposed blocks using witness data provided by executors. The other approach relies on a proof of execution provided by the executor proposing the block and a challenge game, where other executors verify the proof. Both concepts rely on executors for long-term storage of shard chain state.

Cryptocurrencies, such as Bitcoin and 250 similar alt-coins, embody at their core a blockchain protocol –- a mechanism for a distributed network of computational nodes to periodically agree on a set of new transactions. Designing a secure blockchain protocol relies on an open challenge in security, that of designing a highly-scalable agreement protocol open to manipulation by byzantine or arbitrarily malicious nodes. Bitcoin's blockchain agreement protocol exhibits security, but does not scale: it processes 3–7 transactions per second at present, irrespective of the available computation capacity at hand. In this paper, we propose a new distributed agreement protocol for permission-less blockchains called ELASTICO. ELASTICO scales transaction rates almost linearly with available computation for mining: the more the computation power in the network, the higher the number of transaction blocks selected per unit time. ELASTICO is efficient in its network messages and tolerates byzantine adversaries of up to one-fourth of the total computational power. Technically, ELASTICO uniformly partitions or parallelizes the mining network (securely) into smaller committees, each of which processes a disjoint set of transactions (or "shards"). While sharding is common in non-byzantine settings, ELASTICO is the first candidate for a secure sharding protocol with presence of byzantine adversaries. Our scalability experiments on Amazon EC2 with up to \$1, 600\$ nodes confirm ELASTICO's theoretical scaling properties.

NoSQL databases are easy to scale-out because of their flexible schema and support for BASE (Basically Available, Soft State and Eventually Consistent) properties. The process of scaling-out in most of these databases is supported by sharding which is considered as the key feature in providing faster reads and writes to the database. However, securing the data sharded over various servers is a challenging problem because of the data being distributedly processed and transmitted over the unsecured network. Though, extensive research has been performed on NoSQL sharding mechanisms but no specific criterion has been defined to analyze the security of sharded architecture. This paper proposes an assessment criterion comprising various security features for the analysis of sharded NoSQL databases. It presents a detailed view of the security features offered by NoSQL databases and analyzes them with respect to proposed assessment criteria. The presented analysis helps various organizations in the selection of appropriate and reliable database in accordance with their preferences and security requirements.