A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> Cognitive radios, which are capable of sensing their surrounding environment and adapting their internal parameters, have been considered in mobile ad hoc networks. Secondary users can cooperatively sense the spectrum to detect the presence of primary users. In this article we present a novel biologically inspired consensus-based cooperative spectrum sensing scheme in CR-MANETs. Our scheme is based on recent advances in consensus algorithms that have taken inspiration from self-organizing behavior of animal groups such as birds, fish, ants, honeybees, and others. Unlike the existing cooperative spectrum sensing schemes, such as the OR-rule or the 1-out-of-N rule, there is no need for a common receiver to do the data fusion for reaching the final decision. A secondary user needs only to set up local interactions without a centralized node in CR-MANETs. Simulation results are presented to show the effectiveness of the proposed scheme. <s> BIB001 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> In this work, we present HIBE and ABE schemes which are "unbounded" in the sense that the public parameters do not impose additional limitations on the functionality of the systems. In all previous constructions of HIBE in the standard model, a maximum hierarchy depth had to be fixed at setup. In all previous constructions of ABE in the standard model, either a small universe size or a bound on the size of attribute sets had to be fixed at setup. Our constructions avoid these limitations. We use a nested dual system encryption argument to prove full security for our HIBE scheme and selective security for our ABE scheme, both in the standard model and relying on static assumptions. Our ABE scheme supports LSSS matrices as access structures and also provides delegation capabilities to users. <s> BIB002 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> This unified treatment of game theory focuses on finding state-of-the-art solutions to issues surrounding the next generation of wireless and communications networks. Future networks will rely on autonomous and distributed architectures to improve the efficiency and flexibility of mobile applications, and game theory provides the ideal framework for designing efficient and robust distributed algorithms. This book enables readers to develop a solid understanding of game theory, its applications and its use as an effective tool for addressing wireless communication and networking problems. The key results and tools of game theory are covered, as are various real-world technologies including 3G networks, wireless LANs, sensor networks, dynamic spectrum access and cognitive networks. The book also covers a wide range of techniques for modeling, designing and analysing communication networks using game theory, as well as state-of-the-art distributed design techniques. This is an ideal resource for communications engineers, researchers, and graduate and undergraduate students. <s> BIB003 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> User, content, and device names as a security primitive have been an attractive approach especially in the context of Information-Centric Networking (ICN) architectures. We leverage Hierarchical Identity Based Encryption (HIBE) to build (content) name-based security mechanisms used for securely distributing content. In contrast to similar approaches, in our system each user maintains his own Private Key Generator used for generating the master secret key and the public system parameters required by the HIBE algorithm. This way our system does not suffer from the key escrow problem, which is inherent in many similar solutions. In order to disseminate the system parameters of a content owner in a fully distributed way, we use blockchains, a distributed, community managed, global list of transactions. <s> BIB004 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> Cloud-centric cognitive cellular networks utilize dynamic spectrum access and opportunistic network access technologies as a means to mitigate spectrum crunch and network demand. However, furnishing a carrier with personally identifiable information for user setup increases the risk of profiling in cognitive cellular networks, wherein users seek secondary access at various times with multiple carriers. Moreover, network access provisioning — assertion, authentication, authorization, and accounting — implemented in conventional cellular networks is inadequate in the cognitive space, as it is neither spontaneous nor scalable. In this paper, we propose a privacy-enhancing user identity management system using blockchain technology which places due importance on both anonymity and attribution, and supports end-to-end management from user assertion to usage billing. The setup enables network access using pseudonymous identities, hindering the reconstruction of a subscriber's identity. Our test results indicate that this approach diminishes access provisioning duration by up to 4x, decreases network signaling traffic by almost 40%, and enables near real-time user billing that may lead to approximately 3x reduction in payments settlement time. <s> BIB005 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> Cloud data provenance is metadata that records the history of the creation and operations performed on a cloud data object. Secure data provenance is crucial for data accountability, forensics and privacy. In this paper, we propose a decentralized and trusted cloud data provenance architecture using blockchain technology. Blockchain-based data provenance can provide tamper-proof records, enable the transparency of data accountability in the cloud, and help to enhance the privacy and availability of the provenance data. We make use of the cloud storage scenario and choose the cloud file as a data unit to detect user operations for collecting provenance data. We design and implement ProvChain, an architecture to collect and verify cloud data provenance, by embedding the provenance data into blockchain transactions. ProvChain operates mainly in three phases: (1) provenance data collection, (2) provenance data storage, and (3) provenance data validation. Results from performance evaluation demonstrate that ProvChain provides security features including tamper-proof provenance, user privacy and reliability with low overhead for the cloud storage applications. <s> BIB006 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> Cognitive cellular networks can enable opportunistic network access but their effectiveness relies on adaptive handoff algorithms. However, in cognitive radio networks the usufructuary rights of a secondary user are rescinded due to the unanticipated appearance of a primary user causing potential service disruption. In order to provide uninterrupted service to a cognitive cellular user, we propose elastic handoff as a composite framework of conventional cellular and voluntary spectrum handoffs. As with spectrum handoff, elastic handoff grants secondary users spectrum access while insulating them against the arrival of primary users. On the other hand, it is similar to cellular handoff in providing secondary users service assurance. The setup also offers users multiple network access choices, and affords carriers the means to generate additional revenue by capitalizing on excess capacity. We use a blockchain-based spectrum exchange and smart contracts to implement elastic handoff. Our tests show that user-initiated elastic handoff may reduce call drops by up to half compared to observations from a conventional cellular market, and network-initiated elastic handoff can improve a carrier's revenue maximization prospects. <s> BIB007 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> As modern vehicle and communication technologies advanced apace, people begin to believe that the Intelligent Transportation System (ITS) would be achievable in one decade. ITS introduces information technology to the transportation infrastructures and aims to improve road safety and traffic efficiency. However, security is still a main concern in vehicular communication systems (VCSs). This can be addressed through secured group broadcast. Therefore, secure key management schemes are considered as a critical technique for network security. In this paper, we propose a framework for providing secure key management within the heterogeneous network. The security managers (SMs) play a key role in the framework by capturing the vehicle departure information, encapsulating block to transport keys and then executing rekeying to vehicles within the same security domain. The first part of this framework is a novel network topology based on a decentralized blockchain structure. The blockchain concept is proposed to simplify the distributed key management in heterogeneous VCS domains. The second part of the framework uses the dynamic transaction collection period to further reduce the key transfer time during vehicles handover. Extensive simulations and analysis show the effectiveness and efficiency of the proposed framework, in which the blockchain structure performs better in term of key transfer time than the structure with a central manager, while the dynamic scheme allows SMs to flexibly fit various traffic levels. <s> BIB008 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> The constant rise of over-the-top video consumption nowadays challenges the current Internet architecture. In this article, we propose a user-centric approach that helps the necessary reshaping of the content delivery ecosystem. We study how blockchain-powered smart contracts and network service chaining can be exploited to support such novel collaboration schemes. Finally, our findings suggest that the proposed solution can complement existing technologies by supporting a wide range of business cases while at the same time significantly reducing costs. <s> BIB009 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> We propose a localized peer-to-peer (P2P) electricity trading model for locally buying and selling electricity among plug-in hybrid electric vehicles (PHEVs) in smart grids. Unlike traditional schemes, which transport electricity over long distances and through complex electricity transportation meshes, our proposed model achieves demand response by providing incentives to discharging PHEVs to balance local electricity demand out of their own self-interests. However, since transaction security and privacy protection issues present serious challenges, we explore a promising consortium blockchain technology to improve transaction security without reliance on a trusted third party. A localized P 2P E lectricity T rading system with CO nsortium blockchai N (PETCON) method is proposed to illustrate detailed operations of localized P2P electricity trading. Moreover, the electricity pricing and the amount of traded electricity among PHEVs are solved by an iterative double auction mechanism to maximize social welfare in this electricity trading. Security analysis shows that our proposed PETCON improves transaction security and privacy protection. Numerical results based on a real map of Texas indicate that the double auction mechanism can achieve social welfare maximization while protecting privacy of the PHEVs. <s> BIB010 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> The prevalence of high performance mobile devices such as smartphones and tablets has brought fundamental changes to existing wireless networks. The growth of multimedia and location-based mobile services has exponentially increased network congestion and the demands for more wireless access. This has led to the development of advanced techniques to address the resulting challenges based on the concept of cooperation in various heterogeneous network scenarios. Thus, innovative incentive mechanisms in wireless networks are needed to ensure the participation of third party nodes, such as access points, small cells, and users. In this tutorial, we demonstrate the effectiveness of contract theory to design incentive mechanisms for a wide range of application scenarios in wireless networks. In contract theory, participants are offered properly designed rewards based on their performances to encourage better participation. First, we present an overview of basic concepts and models of contract theory, with comparisons to other related methods from economics. We then discuss incentive mechanisms, with a focus on the design of rewards in a contract. We demonstrate how contract theory can be utilized for developing effective incentive mechanisms for emerging wireless network scenarios such as traffic offloading, mobile crowdsourcing, and spectrum trading. <s> BIB011 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> Blockchains enable tamper-proof, ordered logging for transactional data in a decentralized manner over open-access, overlay peer-to-peer networks. In this paper, we propose a decentralized framework of proactive caching in a hierarchical wireless network based on blockchains. We employ the blockchain-based smart contracts to construct an autonomous content caching market. In the market, the cache helpers are able to autonomously adapt their caching strategies according to the market statistics obtained from the blockchain, and the truthfulness of trustless nodes are financially enforced by smart contract terms. Further, we propose an incentive-compatible consensus mechanism based on proof-of-stake to financially encourage the cache helpers to stay active in service. We model the interaction between the cache helpers and the content providers as a Chinese restaurant game. Based on the theoretical analysis regarding the Nash equilibrium of the game, we propose a decentralized strategy-searching algorithm using sequential best response. The simulation results demonstrate both the efficiency and reliability of the proposed equilibrium searching algorithm. <s> BIB012 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> Prior research has proposed technical solutions to use peer-to-peer (P2P) content delivery to serve Internet video, showing that it can reduce costs to content providers. Yet, such methods have not become widespread except for a few niche instances. An important challenge is incentivization: what tangible benefits does P2P content delivery offer users who bring resources to the table? In this paper, we ask whether monetary incentives can help attract peers in P2P content delivery systems. We commissioned a professional survey of people around theUnited States to answer several relevant questions. We found that 51% of the 876 respondents--substantially larger than our expectations--answered"yes"to whether they would participate for suitable financial incentives. Encouraged by the results of the survey, we propose Gringotts, a system to structure incentives and securely incorporate P2P delivery into content delivery systems. Gringotts provides a novel Proof of Delivery mechanism that allows content providers to verify correct delivery of their files, and shows how to use cryptocurrency to pay peers while guarding against liars and Sybil attacks. <s> BIB013 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> Edge computing has great potential to address the challenges in mobile vehicular networks by transferring partial storage and computing functions to network edges. However, it is still a challenge to efficiently utilize heterogeneous edge computing architectures and deploy large-scale IoV systems. In this article, we focus on the collaborations among different edge computing anchors and propose a novel collaborative vehicular edge computing framework, called CVEC. Specifically, CVEC can support more scalable vehicular services and applications by both horizontal and vertical collaborations. Furthermore, we discuss the architecture, principle, mechanisms, special cases, and potential technical enablers to support the CVEC. Finally, we present some research challenges as well as future research directions. <s> BIB014 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> Information from surveillance video is essential for situational awareness (SAW). Nowadays, a prohibitively large amount of surveillance data is being generated continuously by ubiquitously distributed video sensors. It is very challenging to immediately identify the objects of interest or zoom in suspicious actions from thousands of video frames. Making the big data indexable is critical to tackle this problem. It is ideal to generate pattern indexes in a real-time, on-site manner on the video streaming instead of depending on the batch processing at the cloud centers. The modern edge-fog-cloud computing paradigm allows implementation of time sensitive tasks at the edge of the network. The on-site edge devices collect the information sensed in format of frames and extracts useful features. The near-site fog nodes conduct the contextualization and classification of the features. The remote cloud center is in charge of more data intensive and computing intensive tasks. However, exchanging the index information among devices in different layers raises security concerns where an adversary can capture or tamper with features to mislead the surveillance system. In this paper, a blockchain enabled scheme is proposed to protect the index data through an encrypted secure channel between the edge and fog nodes. It reduces the chance of attacks on the small edge and fog devices. The feasibility of the proposal is validated through intensive experimental analysis. <s> BIB015 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> Nowadays, more and more companies migrate business from their own servers to the cloud. With the influx of computational requests, datacenters consume tremendous energy every day, attracting great attention in the energy efficiency dilemma. In this paper, we investigate the energy-aware resource management problem in cloud datacenters, where green energy with unpredictable capacity is connected. Via proposing a robust blockchain-based decentralized resource management framework, we save the energy consumed by the request scheduler. Moreover, we propose a reinforcement learning method embedded in a smart contract to further minimize the energy cost. Because the reinforcement learning method is informed from the historical knowledge, it relies on no request arrival and energy supply. Experimental results on Google cluster traces and real-world electricity price show that our approach is able to reduce the datacenters cost significantly compared with other benchmark algorithms. <s> BIB016 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> In this article, we propose a blockchain verification protocol as a method for enabling and securing spectrum sharing in moving cognitive radio (CR) networks. The spectrum-sharing mechanism is used as a medium-access protocol for accessing wireless bandwidth among competing CRs. We introduce a virtual currency, called Specoins, for payment to access the spectrum. An auction mechanism based on a first-come-first-served queue is used, with the price for the spectrum advertised by each primary user in a decentralized fashion. The blockchain protocol facilitates the transactions between primary and secondary users and is used to validate and save each user's virtual wallet. Also important for mobile networks, the blockchain serves as a distributed database that is visible by all participating parties, and any node can volunteer to update the blockchain. The volunteer nodes are called miners, and they are awarded with Specoins. We propose diverse methods to exchange the Specoins to make leasing possible even by CRs that are not miners. We show the improvement of the proposed algorithm compared with the conventional Aloha medium-access protocol in terms of spectrum usage. This difference is investigated using small-scale fading variation in the wireless channel to compare the performance of our secure method with the conventional medium access used in vehicular communications. The secure blockchain verification protocol is not only secure but also outperforms the conventional system in moderate cases of small-scale fading. In the case of severe small-scale fading, the blockchain protocol will outperform the conventional system if multipath diversity is not used. <s> BIB017 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> The ultra-dense network (UDN) is one of the most promising technologies in the fifth generation (5G) to address the network system capacity issue. However, it is a new challenge that the user equipment (UE) secure access UDN composed of the access points (APs) which characterized with autonomy, temporary, and dynamic. In 5G UDN, the APs are independent and equal. The UDN can be regarded as a decentralized access network. Compared with the traditional base station, the AP has a smaller coverage. There has an issue that the interaction between the UE and APs will be more frequent when UE moves. However, the existing 4G authentication and key agreement algorithm cannot adapt to this fast and frequent authentication requirement. If the UE moves smoothly in a trusted APs group (APG) without frequent authentication, this problem will be solved very well. In order to achieve this goal, we propose a security authentication scheme of 5G UDN based on the block chaining technologies. In this paper, an APG-PBFT algorithm based on the block chaining technology with Byzantine fault tolerance (PBFT) consensus algorithm is proposed. In the algorithm, the consensus mechanism will be optimized and a new reverse screening method will be embedded. In our solution, a trusted chain APG can be generated with APs by APG-PBFT algorithm, and the authentication results can be shared in the APG using the blockchain message propagation mechanism. The principle of fast authentication with APG-PBFT algorithm is present in this paper. The scheme can reduce the authentication frequency when UE moves among the APs and improve the access efficiency. Finally, we analyze the performance of APG-PBFT algorithm and compare it with the traditional PBFT algorithm. The simulation results show that the APG-PBFT algorithm can improve the APG generation efficiency and reduce the authentication frequency of UE, which will be valuably applied to the UDN environment. <s> BIB018 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> The recent expansion of the Internet of Things (IoT) and the consequent explosion in the volume of data produced by smart devices have led to the outsourcing of data to designated data centers. However, to manage these huge data stores, centralized data centers, such as cloud storage cannot afford auspicious way. There are many challenges that must be addressed in the traditional network architecture due to the rapid growth in the diversity and number of devices connected to the internet, which is not designed to provide high availability, real-time data delivery, scalability, security, resilience, and low latency. To address these issues, this paper proposes a novel blockchain-based distributed cloud architecture with a software defined networking (SDN) enable controller fog nodes at the edge of the network to meet the required design principles. The proposed model is a distributed cloud architecture based on blockchain technology, which provides low-cost, secure, and on-demand access to the most competitive computing infrastructures in an IoT network. By creating a distributed cloud infrastructure, the proposed model enables cost-effective high-performance computing. Furthermore, to bring computing resources to the edge of the IoT network and allow low latency access to large amounts of data in a secure manner, we provide a secure distributed fog node architecture that uses SDN and blockchain techniques. Fog nodes are distributed fog computing entities that allow the deployment of fog services, and are formed by multiple computing resources at the edge of the IoT network. We evaluated the performance of our proposed architecture and compared it with the existing models using various performance measures. The results of our evaluation show that performance is improved by reducing the induced delay, reducing the response time, increasing throughput, and the ability to detect real-time attacks in the IoT network with low performance overheads. <s> BIB019 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> With the explosive growth of smart IoT devices at the edge of the Internet, embedding sensors on mobile devices for massive data collection and collective environment sensing has been envisioned as a cost-effective solution for IoT applications. However, existing IoT platforms and framework rely on dedicated middleware for (semi-) centralized task dispatching, data storage and incentive provision. Consequently, they are usually expensive to deploy, have limited adaptability to diverse requirements, and face a series of data security and privacy issues. In this paper, we employ permissionless blockchains to construct a purely decentralized platform for data storage and trading in a wireless-powered IoT crowdsensing system. In the system, IoT sensors use power wirelessly transferred from RF-energy beacons for data sensing and transmission to an access point. The data is then forwarded to the blockchain for distributed ledger services, i.e., data/transaction verification, recording, and maintenance. Due to coupled interference of wireless transmission and transaction fee incurred from blockchain's distributed ledger services, rational sensors have to decide on their transmission rates to maximize individual utility. Thus, we formulate a noncooperative game model to analyze this competitive situation among the sensors. We provide the analytical condition for the existence of the Nash equilibrium as well as a series of insightful numerical results about the equilibrium strategies in the game. <s> BIB020 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> Crowdsensing applications utilize the pervasive smartphone users to collect large-scale sensing data efficiently. The quality of sensing data depends on the participation of highly skilled users. To motivate these skilled users to participate, they should receive enough rewards for compensating their resource consumption. Available incentive mechanisms mainly consider the truthfulness of the mechanism, but mostly ignore the issues of security and privacy caused by a “trustful” center. In this paper, we propose a privacy-preserving blockchain incentive mechanism in crowdsensing applications, in which a cryptocurrency built on blockchains is used as a secure incentive way. High quality contributors will get their payments that are recorded in transaction blocks. The miners will verify the transaction according to the sensing data assessment criteria published by the server. As the transaction information can disclose users’ privacy, a node cooperation verification approach is proposed to achieve $k$ -anonymity privacy protection. Through theoretical analysis and simulation experiments, we show the feasibility and security of our incentive mechanism. <s> BIB021 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> Smart grids equipped with bi-directional communication flow are expected to provide more sophisticated consumption monitoring and energy trading. However, the issues related to the security and privacy of consumption and trading data present serious challenges. In this paper we address the problem of providing transaction security in decentralized smart grid energy trading without reliance on trusted third parties. We have implemented a proof-of-concept for decentralized energy trading system using blockchain technology, multi-signatures, and anonymous encrypted messaging streams, enabling peers to anonymously negotiate energy prices and securely perform trading transactions. We conducted case studies to perform security analysis and performance evaluation within the context of the elicited security and privacy requirements. <s> BIB022 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> In industrial Internet of things (IIoT), peer-to-peer (P2P) energy trading ubiquitously takes place in various scenarios, e.g., microgrids, energy harvesting networks, and vehicle-to-grid networks. However, there are common security and privacy challenges caused by untrusted and nontransparent energy markets in these scenarios. To address the security challenges, we exploit the consortium blockchain technology to propose a secure energy trading system named energy blockchain. This energy blockchain can be widely used in general scenarios of P2P energy trading getting rid of a trusted intermediary. Besides, to reduce the transaction limitation resulted from transaction confirmation delays on the energy blockchain, we propose a credit-based payment scheme to support fast and frequent energy trading. An optimal pricing strategy using Stackelberg game for credit-based loans is also proposed. Security analysis and numerical results based on a real dataset illustrate that the proposed energy blockchain and credit-based payment scheme are secure and efficient in IIoT. <s> BIB023 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> Vehicular networks enable vehicles to generate and broadcast messages in order to improve traffic safety and efficiency. However, due to the nontrusted environments, it is difficult for vehicles to evaluate the credibilities of received messages. In this paper, we propose a decentralized trust management system in vehicular networks based on blockchain techniques. In this system, vehicles can validate the received messages from neighboring vehicles using Bayesian Inference Model. Based on the validation result, the vehicle will generate a rating for each message source vehicle. With the ratings uploaded from vehicles, roadside units (RSUs) calculate the trust value offsets of involved vehicles and pack these data into a “block.” Then, each RSU will try to add their “blocks” to the trust blockchain which is maintained by all the RSUs. By employing the joint proof-of-work (PoW) and proof-of-stake consensus mechanism, the more total value of offsets (stake) is in the block, the easier RSU can find the nonce for the hash function (PoW). In this way, all RSUs collaboratively maintain an updated, reliable, and consistent trust blockchain. Simulation results reveal that the proposed system is effective and feasible in collecting, calculating, and storing trust values in vehicular networks. <s> BIB024 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> Crowdsourcing systems which utilize the human intelligence to solve complex tasks have gained considerable interest and adoption in recent years. However, the majority of existing crowdsourcing systems rely on central servers, which are subject to the weaknesses of traditional trust-based model, such as single point of failure. They are also vulnerable to distributed denial of service (DDoS) and Sybil attacks due to malicious users involvement. In addition, high service fees from the crowdsourcing platform may hinder the development of crowdsourcing. How to address these potential issues has both research and substantial value. In this paper, we conceptualize a blockchain-based decentralized framework for crowdsourcing named CrowdBC, in which a requester's task can be solved by a crowd of workers without relying on any third trusted institution, users' privacy can be guaranteed and only low transaction fees are required. In particular, we introduce the architecture of our proposed framework, based on which we give a concrete scheme. We further implement a software prototype on Ethereum public test network with real-world dataset. Experiment results show the feasibility, usability, and scalability of our proposed crowdsourcing system. <s> BIB025 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> B. Access Control and Self-Organization <s> The smart community (SC), as an important part of the Internet of Energy (IoE), can facilitate integration of distributed renewable energy sources and electric vehicles (EVs) in the smart grid. However, due to the potential security and privacy issues caused by untrusted and opaque energy markets, it becomes a great challenge to optimally schedule the charging behaviors of EVs with distinct energy consumption preferences in SC. In this paper, we propose a contract-based energy blockchain for secure EV charging in SC. First, a permissioned energy blockchain system is introduced to implement secure charging services for EVs with the execution of smart contracts. Second, a reputation-based delegated Byzantine fault tolerance consensus algorithm is proposed to efficiently achieve the consensus in the permissioned blockchain. Third, based on the contract theory, the optimal contracts are analyzed and designed to satisfy EVs’ individual needs for energy sources while maximizing the operator’s utility. Furthermore, a novel energy allocation mechanism is proposed to allocate the limited renewable energy for EVs. Finally, extensive numerical results are carried out to evaluate and demonstrate the effectiveness and efficiency of the proposed scheme through comparison with other conventional schemes. <s> BIB026
The most popular design approach sees blockchains as enabling technologies for implementing accountable and secure services in a decentralized fashion. In other words, blockchains are utilized as a decentralized intermediary for channeling/accounting services upon demands as well as for guaranteeing data security and confidentiality. In Figure 26 , we describe a generic framework of decentralized service provision built upon blockchains. The most prominent feature of this framework lies in that the interactions between different entities in the system are all tunneled autonomously in the form of smart contracts. Such a framework has been adopted by a wide range of service provision systems including P2P file sharing based on InterPlanetary File System 25 (IPFS) [37], decentralized content delivery BIB012 , BIB013 , access control in telecommunication networks BIB014 , BIB005 and various missions for access and permission management, e.g., in IoTs BIB015 and clouds BIB016 . For different task requirements, this application framework can be expanded by including additional entities, e.g., third-party auditors BIB006 , as well as new operations, e.g., Hierarchical Identity Based Encryption (HIBE, see also BIB002 ) BIB004 . To provide a better idea on how this emerging framework can be shaped in recent studies, we categorize the blockchain-based proposals for self-organization according to the areas or context that they are applied in. 1) Access Control in Wireless Networks: In BIB005 , the authors propose to use blockchains for providing Identity and Credibility Service (ICS) in cloud-centric Cognitive Radio (CR) networks. The CR users utilize their pseudonymous identities on the blockchain to negotiate with the network operator, i.e., the spectrum owner, for granting opportunistic access and settling payment. According to BIB005 , the ICS can be provided by either the blockchain itself or a third-party entity registered on-chain, and the network access negotiation is automated by smart contracts. Meanwhile, it is pointed out in BIB005 that the blockchain's consensus mechanism can be employed for coordinating spectrum sensing among the distributed CR users. However, it is not clear how the CR-user consensus can be achieved on top of the ledger consensus as with the classical methods BIB001 in CR networks. In another study BIB007 , the same authors propose to use a permissioned blockchain to handle the network access exchange, i.e., the spectrum handoffs. The CR users and their base station controller submit the information of spectrum and network utilization as metadata onto the blockchain. Then, the CR network responds by updating the smart contracts and publishing the new access prices and number of network access units allocated to each CR onto the blockchain for execution. A similar design with more technical details can be found in BIB017 . Therein, a blockchain based on the Nakamoto protocol with its embedded tokens and smart contract layer is adopted as a spectrum auction platform. More specifically, multiple primary users as providers sell their unused bands at a certain price with smart contracts and allocate them to responding CR users when the contracts are executed upon certain conditions. It is claimed in BIB017 that the blockchain-based spectrum allocation outperforms the conventional mediumaccess protocols such as Aloha. However, technical details are missing about how the issue of high transaction latency is addressed to satisfy the CR network's constraint due to the timescale of small-scale fading in wireless channels. Blockchains are also introduced into vehicular ad-hoc networks (VANETs) to address the issues of network volatility  https://github.com/ipfs/ipfs. due to high mobility. For Vehicles-to-Infrastructure (V2I) communication, the study in BIB008 uses the Nakamoto-based blockchain as a secure key-delivery channel to handle the access of a moving vehicle to groups of Road Side Units (RSUs) in different regions. By encapsulating the key information in a blockchain transaction, the security manager of one region is responsible for issuing the transactions to that of the new region as well as mining the new blocks onto the blockchain. Comparatively, the study in BIB024 focuses more on the ad-hoc nature of VANETs and employs the blockchain to collect the trustworthiness rating on messages sent to each other by the peer vehicles. The RSUs do not only work as the consensus nodes in the blockchain network but also work as the decentralized storage hosting peers of the trust rating data (cf. Figure 26 ). It is worth noting that in BIB024 the transactions carrying vehicle reports are essentially unspendable. The RSUs employ weighted average to the rating scores to estimate the quality of the received reports. Then, they use the estimation results as the difficulty parameter for PoW-based mining in a similar manner of the Peercoin-like protocols (see also Section V-A). In the existing studies on blockchains-based network access control, the study in BIB018 is among the few to explicitly address the issue of high signaling latency over the blockchain due to the adoption of Nakamoto protocols. In BIB018 , the process of authentication transfer for User Equipments (UEs) in a 5G ultra dense network is handled by a blockchain in a similar way as in BIB007 . Instead of delegating the transaction/contract execution process to a dedicated overlay blockchain, it is proposed in BIB018 that the Access Points (APs) use the PBFT protocol within a dynamic consensus committee to handle the requests of authentication by UEs in the form of transactions or smart contracts. In order to implement the PBFT protocol, a local server center is introduced as the primary peer (i.e., leader) of the committee. Nevertheless, we note that any nonleader consistency protocol can be adopted in this framework to preserve the property of complete decentralization (see also Section VI-B). According to BIB018 , the PBFT-based blockchain is able to keep the transaction delay around 100ms. Compared with the standard Nakamoto protocols, it is more practical to deploy network control mechanisms over PBFT-based blockchains for delay-critical tasks such as access hand-over. However, how to find a balance between the required levels of latency and decentralization (e.g., with hybrid consensus protocols) still remains an open question. 2) Self-Organization and Security Enhancement under Various Network Architectures: Apart from network access control, blockchains have also been applied to various scenarios as a decentralized platform for self-organization. As briefly shown in Section VII-B1, blockchains can also be used for security enhancement with its embedded cryptographic functionalities. Typical examples for the former applications can be found in proactive caching and Content Delivery Networks (CDNs) BIB012 , BIB013 , BIB009 . In BIB013 , a decentralized CDN platform is established with the help of blockchains among the three parties of content providers, content serving peers and clients (cf. Figure 26 ). With smart contracts, the content providers offload the tasks of content delivery to multiple content serving peers. It is suggested in BIB013 that the content providers use smart contract prices to control the file placement on multiple serving peers according to the demand frequency and achievable QoS at the peers. Furthermore, the work in BIB012 mathematically formulates the pricing-response interaction between the providers and the serving peers as a potential game BIB003 Chapter 3.4] . Then, it designs a series of smart contracts for automatically matching the peers to the providers under the same CDN framework. A modified PoS protocol is subsequently proposed to incentivize the serving peers to work as the consensus nodes of the blockchain without consuming significant computational power. In BIB009 , the authors design a blockchain-based brokering platform for video delivery in a user-centric CDN ecosystem. The proposed platform is built upon three independent blockchains for content brokering, delivery monitoring and delivery provisioning, respectively. The content broking blockchain handles the content requests and matches the clients' requests to the providers' offers in a series of smart contracts among the three parties. The delivery monitoring blockchain records proofs of delivery and finalizes the payment and refund between the providers and the clients. The delivery provisioning blockchain provides smart contacts for content dissemination between the providers and the serving peers. In such a framework, the decentralized entities in the CDN treat the blockchain as a ready-to-use service offered by a third party. Therefore, any form of blockchains (e.g., the permissioned HyperLedger) can be employed as long as the requirement of transaction throughput and latency is met. In various applications of edge/fog/cloud computing, more and more attempts are also found to use blockchains for providing services such as trusted auditing and secured data delivery in addition to autonomous brokering. In BIB006 , the blockchain is used as a tamper-proof provenance database on the cloud server side to record the history of the creation and operations performed on a cloud data object. By adopting a public blockchain, any node in the blockchain network is able to perform data auditing. By using pseudonymous identities on blockchains, the proposed auditing mechanism reduces the probability that auditors can correlate the real identity of a specific user with the operations. In other works such as BIB015 , BIB019 , the blockchain is introduced into the threelayer paradigm of edge-fog-cloud computing. In BIB015 , the blockchain is used as a connector to provide encrypted channel by using the public key functionality for data delivery from the edge devices to the fog and cloud. More specifically, the study in BIB015 considers a smart video surveillance network, where the preprocessing tasks such as object tracking are handled at the edge devices, and the more sophisticated tasks of data aggregation and decision making are performed in the fog/cloud based on the data filtered at the edge. To prevent malicious modification on video frames in the untrusted fog layer, the cloud layer deploys smart contracts on the blockchain to provide an indexing service and generate unique index for every video frame with transactions published onto the blockchain. The work in BIB019 adopts the same data-processing flow from the edge to the cloud as in BIB015 . In contrast to BIB015 , the blockchain is used to provide automatic matching between the data-service requests and the providers in the cloud's service provider pool. In this sense, the blockchain is again used to provide the broking service as in BIB012 , BIB013 . 3) Trusted Broking Services in Cyber-Physical Systems: In the context of crowdsourcing (e.g., crowdsourcing of mobile sensors, a.k.a., crowdsensing), permissionless blockchains are also found to be especially appropriate for providing nonmanipulable brokering services between clients (i.e., task requesters) and service providers (i.e., crowdsourcing workers). In BIB025 , a purely decentralized crowdsourcing system for general purpose is proposed following the paradigm described by Figure 26 . In the proposed framework, the procedures of identity registration, task/receiving, reputation rating and reward assignment are all automated in the form of smart contracts. Following the approaches described in Section VII-A, the blockchain network delegates the data storage to an independent storage layer and only keeps the metadata on-chain. Similar blockchain-based frameworks are also adopted for crowdsensing in recent studies such as BIB020 , BIB021 , where additional functionalities are adopted in the blockchain networks to address different performance requirement such as throughput scalability BIB020 and anonymity enhancement BIB021 . In the context of IoTs, blockchain-based infrastructure is also envisioned as a promising alternative of the centralized one for data management, trading automation and privacy protection. In BIB022 , the authors introduce the micro-payment channels (see also Section VI-A) based on a Bitcoin-like blockchain to conduct energy trading in a decentralized smart grid without relying on trusted third parties. In BIB010 , a P2P surplus-energy trading mesh of the plug-in hybrid electric vehicles is built on a Nakamoto protocol-based blockchain. In the proposed framework, a number of authorized nodes are responsible for processing and recording the transactions and an iterative double auction mechanism is deployed based on the transactions published on the blockchain. This framework of blockchains as a P2P trading mediator is also adopted in BIB023 , BIB026 , where the PBFT protocol is used to replace the Nakamoto protocol and form a consortium blockchain. Furthermore, the mathematical tool of contract theory (see BIB011 for more details) is adopted to determine the optimal prices and requested utility in the relevant smart contracts.