IoT (IoT) networks generate massive amounts of data while supporting various applications, where the security and protection of IoT data are very important. In particular, blockchain technology supporting IoT networks is considered as the most secure, expandable, and scalable database storage solution. However, existing blockchain systems have scalability problems due to low throughput and high resource consumption, and security problems due to malicious attacks. Several studies have proposed blockchain technologies that can improve the scalability or the security level, but there have been few studies that improve both at the same time. In addition, most existing studies do not consider malicious attack scenarios in the consensus process, which deteriorates the blockchain security level. In order to solve the scalability and security problems simultaneously, this paper proposes a Dueling Double Deep-Q-network with Prioritized experience replay (D3P) based secure trust-based delegated consensus blockchain (TDCB-D3P) scheme that optimizes the blockchain performance by applying deep reinforcement learning (DRL) technology. The TDCB-D3P scheme uses a trust system with a delegated consensus algorithm to ensure the security level and reduce computing costs. In addition, DRL is used to compute the optimum blockchain parameters under the dynamic network state and maximize the transactions per second (TPS) performance and security level. The simulation results show that the TDCB-D3P scheme can provide a superior TPS and resource consumption performance. Furthermore, in blockchain networks with malicious nodes, the simulation results show that the proposed scheme significantly improves the security level when compared to existing blockchain schemes by effectively reducing the influence of malicious nodes.
Proof of Stake (PoS) based consensus provides a better mechanism than Proof of Work (PoW) consensus for extending the blockchain without significant energy waste. Most of the PoS consensus protocols derive or use some randomness to elect a leader candidate. This makes the consensus weaker and attracts more attackers to mount different attacks, e.g., long-range attacks and block withholding attacks. In PoS consensus, having more stakes gives more chances to be a leader among participating stakeholders. Therefore, most PoS protocols do not provide better fairness for the stakeholders participating in the consensus protocol. Moreover, these protocols suffer from high communication complexity for selecting a leader candidate in each consensus round. In this work, we propose a novel consensus protocol âR3Vâ that selects a set of leader candidates in a round-robin manner according to age. Finally, these leader candidates compete to be the block leader by solving a Verifiable Delay Function (VDF) based puzzle. We propose different methods to generate verifiable identities for the stakeholders. The identities are enrolled in the blockchain, which provides the age norm needed for the consensus. Compared with the other PoS consensus protocols, our protocol shows better resilience against most of the common attacks on PoS protocols. Additionally, it proclaims low energy consumption, less communication complexity, and better fairness.
The efficiency of block lifecycle determines the performance of blockchain, which is critically affected by the execution, mining and validation steps in blockchain lifecycle. To accelerate blockchains, many works focus on optimizing the mining step while ignoring other steps. In this paper, we propose a novel blockchain framework-FastBlock to speed up the execution and validation steps by introducing efficient concurrency. To efficiently prevent the potential concurrency violations, FastBlock utilizes symbolic execution to identify minimal atomic sections in each transaction and guarantees the atomicity of these sections in execution step via an efficient concurrency control mechanism-hardware transactional memory (HTM). To enable a deterministic validation step, FastBlock concurrently re-executes transactions based on a happen-before graph without increasing block size. Finally, we implement FastBlock and evaluate it in terms of conflicting transactions rate, number of transactions per block, and varying thread number. Our results indicate that FastBlock is efficient: the execution step and validation step speed up to 3.0x and 2.3x on average over the original serial model respectively with eight concurrent threads.
Minsu Kim, Sungho Lee, Chanwon Park, Jemin Lee ¡ 5 authors
The Age of Information (AoI) is a recently proposed metric for quantifying data freshness in real-time status monitoring systems, where timeliness is of importance. In this article, the problem of characterizing and controlling the AoI is studied in the context of blockchain-enabled monitoring networks (BeMNs). In BeMN, status updates from sources are transmitted and recorded in a blockchain. To investigate the statistical characteristics of the AoI in BeMN, the transmission latency and the consensus latency are first rigorously modeled. Then, the average AoI, the AoI violation probability, and the peak AoI violation probability are derived in a closed form so as to quantify the performance of BeMN. Furthermore, a simplified form is derived for the AoI violation probability, and it is shown that this quantity can capture the upper or lower bounds of the actual AoI violation probability. Simulation results show that each BeMN parameters (i.e., target successful transmission probability, block size, and timeout) can have conflicting effects on the AoI-related performance. Subsequently, design insights are provided to maintain the freshness of the status data in BeMN. Then, experimental results with a real Hyperledger Fabric platform further validate the accuracy of our modeling and analysis.
Blockchain protocols differ in fundamental ways, including the mechanics of selecting users to produce blocks (e.g., proof-of-work vs. proof-of-stake) and the method to establish consensus (e.g., longest chain rules vs. Byzantine fault-tolerant (BFT) inspired protocols). These fundamental differences have hindered "apples-to-apples" comparisons between different categories of blockchain protocols and, in turn, the development of theory to formally discuss their relative merits. This paper presents a parsimonious abstraction sufficient for capturing and comparing properties of many well-known permissionless blockchain protocols, simultaneously capturing essential properties of both proof-of-work (PoW) and proof-of-stake (PoS) protocols, and of both longest-chain-type and BFT-type protocols. Our framework blackboxes the precise mechanics of the user selection process, allowing us to isolate the properties of the selection process that are significant for protocol design. We demonstrate the utility of our general framework with several concrete results: 1. We prove a CAP-type impossibility theorem asserting that liveness with an unknown level of participation rules out security in a partially synchronous setting. 2. Delving deeper into the partially synchronous setting, we prove that a necessary and sufficient condition for security is the production of "certificates," meaning stand-alone proofs of block confirmation. 3. Restricting to synchronous settings, we prove that typical protocols with a known level of participation (including longest chain-type PoS protocols) can be adapted to provide certificates, but those with an unknown level of participation cannot. 4. Finally, we use our framework to articulate a modular two-step approach to blockchain security analysis that effectively reduces the permissionless case to the permissioned case.
Yixin Li, Bin Cao, Liang Liang, Lei Zhang ¡ 6 authors
Blockchain, a distributed ledger technology, has attracted many attentions to enable a decentralized and safe wireless networks for various applications. Considering the high density of nodes and the massive service requests in next-generation wireless network will result in a surge of blockchain forking, this paper proposes a Block Access Control (BAC) approach to address forking problem and transmit block effectively while improving transaction throughput and saving computational power. Then, using a Markov chain model, we analyse the performance of a wireless blockchain network by involving the effect of BAC approach. The results show that the BAC approach can help the network to achieve a high transaction throughput while addressing forking problem.
Distributed Ledgers and Blockchains involve decentralized networking technologies such as peer-to-peer networks. Both permissioned and unpermissioned blockchains are designed to tolerate and to overcome the failure of individual nodes, which need to update themselves once they reconnect to the blockchain network. At the same time, it is important to avoid accidental network partitioning, since partitioning can lead to inconsistent "multiple truths" and violate the shared consensus about the global state, which must be maintained across all active and re-emerging nodes. In general, reconciling inconsistent "multiple truths" would require the deletion of information which was persisted to the blockchain (in one of the network partitions), and such removal violates the core blockchain principle of audit-proof and tamper-proof "write once read many" access (WORM). However, current mainstream implementations such as Ethereum do not protect against network partitioning (either by accident or caused by an attack), and there is no research on how the consensus implementations behave in the presence of network partitioning. Given the differences in design and implementation across ledgers and blockchains, a systematic analytic approach must be established before partitioning prevention in specific products is studied. The contribution of this paper is a foundational analysis of enterprise-grade consensus protocols, including design recommendations for partitioning avoidance for Proof-of-Authority in Hyperledger Fabric. We also survey related work and lay out next research steps.
Recent advances in blockchain technology have led to a significant interest in developing blockchain-based applications. While data can be retained in a blockchain, the stored values can be deleted or updated. From a user viewpoint that searches for data, it is unclear whether the discovered data from the blockchain storage is relevant for real-time decision-making processes for block-chain-based applications. The data freshness issue serves as a critical factor, especially in dynamic networks handling real-time information. In general, transactions to renew data require additional processing time inside the blockchain network, which is called ledger-commitment latency. Due to this problem, some users may receive outdated data. As a result, it is important to investigate if the blockchain is suitable for providing real-time data services. In this article, we first describe block-chain-enabled (BCE) networks with Hyperledger Fabric (HLF). Then, we define age-of-information (AoI) of BCE networks and investigate influential factors on this AoI. Experiments are conducted to explore the impacts of the influential factors on data freshness in BCE networks. Lastly, we conclude by discussing future challenges.
In blockchain applications, transaction latency is crucial for determining the quality of service (QoS). Transaction latency is measured as the time between its issuance and its inclusion in a block in the chain. When different applications use the same blockchain network, a block proposer often prioritizes its own application transactions over other applications transactions to minimize its own latency. To maintain fairness, a block proposer is typically supposed to select the included transactions randomly providing each transaction similar chances to be included. The random selection might cause some transactions to experience high latency since this selection implies a high variance in the time a transaction waits until it is selected. We suggest an alternative, age-aware approach towards fairness so that transaction priority is increased upon observing a large waiting time. The challenge with this approach is that the age of a transaction is not absolute due to transaction propagation. Moreover, a node might present its transactions as older to obtain priority. We consider three network restrictions on transaction propagation and explain how to enhance fairness in each one of them. We describe three declaration schemes in which a node declares its pending transactions providing the ability to validate transaction age. We demonstrate the advantages of the solutions on Ethereum and synthetic data in reducing tail latency.
Vicent Cholvi, Antonio Fernåndez Anta, Chryssis Georgiou, Nicolas Nicolaou ¡ 5 authors
A Distributed Ledger Object (DLO) is a concurrent object that maintains a totally ordered sequence of records, and supports two basic operations: append, which appends a record at the end of the sequence, and get, which returns the sequence of records. In this work we provide a proper formalization of a Byzantine-tolerant Distributed Ledger Object (BDLO), which is a DLO in a distributed system in which processes may deviate arbitrarily from their indented behavior, i.e. they may be Byzantine. Our formal definition is accompanied by algorithms to implement BDLOs by utilizing an underlying Byzantine Atomic Broadcast service. We then utilize the BDLO implementations to solve the Atomic Appends problem against Byzantine processes. The Atomic Appends problem emerges when several clients have records to append, the record of each client has to be appended to a different BDLO, and it must be guaranteed that either all records are appended or none. We present distributed algorithms implementing solutions for the Atomic Appends problem when the clients (which are involved in the appends) and the servers (which maintain the BDLOs) may be Byzantine.
As a new form of network, the Internet of things (IoT) is becoming more widely used in peopleâs lives. In this paper, related theoretical research and practical applications of the IoT are explored. The security of the IoT has become a hot research topic. Access controls are methods that control reasonable allocations of data and resources and ensure the security of the IoT. However, most access control systems do not dynamically assign usersâ rights. Additionally, with some access control systems, there is a risk of overstepping other userâs authority, and there may exist a central authority that is a single point of failure. Therefore, to solve these problems, this paper proposes a Task-Attribute-Based Access Control scheme for the IoT via blockchain that combines the access control technologies of both the IoT and blockchain. This model, which merges the advantages of task-based access controls and attribute-based access controls, is perfectly integrated with blockchain technology. This model uses hash functions and digital signature algorithms to ensure the authenticity and integrity of the data, and it can dynamically allocate usersâ minimum privileges and thus perfectly solves the single point of failure problem. The model is implemented using a Geth client and solidity code, and the simulation results demonstrate the effectiveness of the model.
Blockchain is maintained as a global log between a network of nodes and uses cryptographic distributed protocols to synchronize the updates. As adopted by Bitcoin and Ethereum these update operations to the ledger are serialized, and executed in batches. To safeguard the system against the generation of conflicting sets of updates and maintain the consistency of the ledger, the frequency of the updates is controlled, which severely affects the performance of the system. This paper presents Converging Directed Acyclic Graph (CDAG), as a substitute for the chain and DAG structures used in other blockchain protocols. CDAG allows multiple parallel updates to the ledger and converges them at the next step providing finality to the blocks. It partitions the updates into non-intersecting buckets of transactions to prevent the generation of conflicting blocks and divide the time into slots to provide enough time for them to propagate in the network. Multiple simultaneous updates improve the throughput of CDAG, and the converging step helps to finalize them faster, even in the presence of conflicts. Moreover, CDAG provides a total order among the blocks of the ledger to support smart contracts, unlike some of the other blockDAG protocols. We evaluate the performance of CDAG on Google Cloud Platform using Google Kubernetes Engine, simulating a real-time network. Experimental results show that CDAG achieves a throughput of more than 2000 transactions per second and confirms them well in under 2 minutes. Also, the protocol scales well in comparison to other permissioned protocols, and the capacity of the network only limits the performance.
To implement a blockchain, the trend is now to integrate a non-trivial Byzantine fault tolerant consensus algorithm instead of the seminal idea of waiting to receive blocks to decide upon the longest branch. After a decade of existence, blockchains trade now large amounts of valuable assets and a simple disagreement could lead to disastrous losses. Unfortunately, Byzantine consensus solutions used in blockchains are at best proved correct "by hand" as we are not aware of any of them having been formally verified. In this paper, we propose two contributions: (i) we illustrate the severity of the problem by listing six vulnerabilities of blockchain consensus including two new counter-examples; (ii) we then formally verify two Byzantine fault tolerant components of Red Belly Blockchain using the ByMC model checker. First, we specify a simple broadcast primitive in 116 lines of code that is verified in 40 seconds on a 2-core Intel machine. Then, we specify a blockchain consensus algorithm in 276 lines of code that is verified in 17 minutes on a 64-core AMD machine using MPI. To conclude, we argue that it has now become both relatively simple and crucial to formally verify the correctness of blockchain consensus protocols.
In his talk, Bela Gipp, Professor for Data & Knowledge Engineering at the University of Wuppertal, presented the blockchain-based trusted timestamping service Origin-Stamp. Bela developed OriginStamp as a Ph.D. student in 2012, as no convenient and tamper-proof method existed to create timestamps. Since then, OriginStamp has been used over 6 million times by researchers, journalists in war regions, pharmaceutical companies, and individuals. Use cases are the timestamping of ideas for patent applications, timestamping of digital archives or timestamping of pre-existing damage, e.g., when hiring a rental car. The service can be used via a website, mobile phone apps, or an API, which allows developers to easily make use of trusted timestamping in their own applications. Trusted timestamping is the process of securely tracing the creation and modification time of any digital file. In contrast to conventional commercial timestamping authorities, OriginStamp uses the blockchain of the cryptocurrency Bitcoin as a decentralized, tamper-proof, and cost-efficient timestamping authority. To try it yourself, visit www.originstamp.org.
Mohammad M. Jalalzai, Costas Busch, Golden G. Richard
Byzantine Fault Tolerant (BFT) consensus exhibits higher throughput in comparison to Proof of Work (PoW) in blockchains. However, BFT-based protocols suffer from scalability problems with respect to the number of replicas in the network due to their inherent quadratic message complexity. Previously, proposed solutions improve BFT performance for normal operation, but will fall back to quadratic message complexity once the protocol observes a certain number of failures. To address this issue we propose Proteus, a new BFT-based consensus protocol which elects a subset of nodes c as a root committee. Proteus guarantees stable performance, regardless of the number of failures in the network and it improves on the quadratic message complexity of typical BFT-based protocols to O(cn) messages, where c << n, for large number of nodes n. We tested our protocol on 200 Amazon EC2 instances, with two different baseline BFT protocols (PBFT and Bchain) for comparison. In these tests, our protocol outperformed the baselines by more than 2Ă in terms of throughput as well as latency.
Blockchain protocols based on Proof-of-Stake (PoS) algorithms aim to provide an alternative to the energy-consuming Proof-of-Work mining procedure. Following a PoS algorithm, nodes have to agree on the miner next eligible to contribute a block and on the point in time he is allowed to broadcast it. The latter requirement raises to the need for synchronous clocks. In this paper we describe BeaconBlocks, a new scheme for constructing PoS protocols. A major difference to former work is incorporating time synchronization as an essential element of the protocol itself, gaining independence of the nodes' clocks and allowing the protocol to resist attacks on clock synchronization infrastructure. To this end, we describe both a mechanism for obtaining the correct time during node startup and for retaining synchronicity of estimated time during a node's lifetime. In contrast to prior work, our approach for miner selection exhibits an interleaved unslotted structure. We show that fairness is achieved when miners follow our scheme and we provide a discussion of attack possibilities, allowing developers to choose secure parameters when adopting the scheme.
Summary Contemporary blockchain such as Bitcoin and Ethereum execute transactions serially by miners and validators and determine the ProofâofâWork (PoW). Such serial execution is unable to exploit modern multiâcore resources efficiently, hence limiting the system throughput and increasing the transaction acceptance latency. The objective of this work is to increase the transaction throughput by introducing parallel transaction execution using a static analysis over the transaction dependencies. We propose the DiPETrans framework for distributed execution of transactions in a block. Here, peers in the blockchain network form a community of trusted nodes to execute the transactions and find the PoW inâparallel, using a leaderâfollower approach. During mining, the leader statically analyzes the transactions, creates different groups (shards) of independent transactions, and distributes them to followers to execute concurrently. After execution, the community's compute power is utilized to solve the PoW concurrently. When a block is successfully created, the leader broadcasts the proposed block to other peers in the network for validation. On receiving a block, the validators reâexecute the block transactions and accept the block if they reach the same state as shared by the miner. Validation can also be done in parallel, following the same leaderâfollower approach as mining. We report experiments using over 5 million real transactions from the Ethereum blockchain and execute them using our DiPETrans framework to empirically validate the benefits of our techniques over a traditional sequential execution. We achieve a maximum speedup of 2.2 and 2.0 and an average speedup of 1.6 and 1.5 for the miner and the validator, respectively, with 100â500 transactions per block when using 6 machines in the community. Further, we achieve a peak of 5 endâtoâend block creation speedup using a parallel miner over a serial miner.
Chrysoula Stathakopoulou, Tudor David, Matej PavloviÄ, Marko VukoliÄ
This paper presents Mir-BFT, a robust Byzantine fault-tolerant (BFT) total order broadcast protocol aimed at maximizing throughput on wide-area networks (WANs), targeting deployments in decentralized networks, such as permissioned and Proof-of-Stake permissionless blockchain systems. Mir-BFT is the first BFT protocol that allows multiple leaders to propose request batches independently (i.e., parallel leaders), in a way that precludes request duplication attacks by malicious (Byzantine) clients, by rotating the assignment of a partitioned request hash space to leaders. As this mechanism removes a single-leader bandwidth bottleneck and exposes a computation bottleneck related to authenticating clients even on a WAN, our protocol further boosts throughput using a client signature verification sharding optimization. Our evaluation shows that Mir-BFT outperforms state-of-the-art and orders more than 60000 signed Bitcoin-sized (500-byte) transactions per second on a widely distributed 100 nodes, 1 Gbps WAN setup, with typical latencies of few seconds. We also evaluate Mir-BFT under different crash and Byzantine faults, demonstrating its performance robustness. Mir-BFT relies on classical BFT protocol constructs, which simplifies reasoning about its correctness. Specifically, Mir-BFT is a generalization of the celebrated and scrutinized PBFT protocol. In a nutshell, Mir-BFT follows PBFT "safety-wise", with changes needed to accommodate novel features restricted to PBFT liveness.
A key issue for Distributed Ledger Technologies is how to agree on any changes to the Ledger; the way to reach such an agreement is known as consensus protocol. There are currently many platforms and implementations of DLTs, each offering a more or less effective way to reach consensus. As a result, it is sometimes difficult to know which consensus mechanism is most appropriate for a given use case. We propose in this short paper a draft methodology to choose between a lottery-based consensus and a voting-based consensus. We take in account several indicators, both related to the requirements of the use case in question, but also to its position relatively to the tradeoff âSecurity - Scalability - Decentralizationâ.
Holger Kinkelin, Heiko Niedermayer, Marc MĂźller, Georg Carle
Configuration management in networks with highest security demands must not depend on just one administrator and her device. Otherwise, problems can be caused by mistakes or malicious behavior of this admin, or when her computer got compromised, which allows an attacker to abuse the administrator's far-reaching permissions. Instead, we propose to use a reliable and resilient configuration management process orchestrated by a configuration management system (CMS). This can be achieved by separation of concerns (proposing a configuration vs. authorizing it), employing multi-party authorization (MPA), and enforcing that only authorized configurations can be deployed. This results in a configuration management process that is decentralized on a human, decision-making level, and a technical, device level. However, due to different opinions or adversarial interference, the result of an MPA process can end in a conflict. This raises the question how such conflicts can be mediated in a better way than just employing majority voting, which is insufficient in certain situations. As an alternative, this paper introduces building blocks of customizable conflict mediation strategies which we integrated into our CMS TANCS . The conflict mediation functionality as well as the initial TANCS implementation run on top of the distributed ledger and smart contract framework Hyperledger Fabric which makes all processes resilient and tamper-resistant.