Benedikt Bünz, Lucianna Kiffer, Loi Luu, Mahdi Zamani
To validate transactions, cryptocurrencies such as Bitcoin and Ethereum require nodes to verify that a blockchain is valid. This entails downloading and verifying all blocks, taking hours and requiring gigabytes of bandwidth and storage. Hence, clients with limited resources cannot verify transactions independently without trusting full nodes. Bitcoin and Ethereum offer light clients known as simplified payment verification (SPV) clients, that can verify the chain by downloading only the block headers. Unfortunately, the storage and bandwidth requirements of SPV clients still increase linearly with the chain length. For example, as of July 2019, an SPV client in Ethereum needs to download and store about 4 GB of data.Recently, Kiayias et al. proposed a solution known as noninteractive proofs of proof-of-work (NIPoPoW) that allows a light client to download and store only a polylogarithmic number of block headers in expectation. Unfortunately, NIPoPoWs are succinct only as long as no adversary influences the honest chain, and can only be used in chains with fixed block difficulty, contrary to most cryptocurrencies which adjust block difficulty frequently according to the network hashrate.We introduce FlyClient, a novel transaction verification light client for chains of variable difficulty. FlyClient is efficient both asymptotically and practically and requires downloading only a logarithmic number of block headers while storing only a single block header between executions. Using an optimal probabilistic block sampling protocol and Merkle Mountain Range (MMR) commitments, FlyClient overcomes the limitations of NIPoPoWs and generates shorter proofs over all measured parameters. In Ethereum, FlyClient achieves a synchronization proof size of less than 500 KB which is roughly 6,600x smaller than SPV proofs. We finally discuss how FlyClient can be deployed with minimal changes to the existing cryptocurrencies via an uncontentious velvet fork.
Federated learning has the potential to make machine learning applicable to highly privacy-sensitive domains and distributed datasets. In some scenarios, however, a central server for aggregating the partial learning results is not available. In fully decentralized learning, a network of peer-to-peer nodes collaborates to form a consensus on a global model without a trusted aggregating party. Often, the network consists of Internet of Things (IoT) and Edge computing nodes.Previous approaches for decentralized learning map the gradient batching and averaging algorithm from traditional federated learning to blockchain architectures. In an open network of participating nodes, the threat of adversarial nodes introducing poisoned models into the network increases compared to a federated learning scenario which is controlled by a single authority. Hence, the decentralized architecture must additionally include a machine learning-aware fault tolerance mechanism to address the increased attack surface.We propose a tangle architecture for decentralized learning, where the validity of model updates is checked as part of the basic consensus. We provide an experimental evaluation of the proposed architecture, showing that it performs well in both model convergence and model poisoning protection.
Philipp Schindler, Aljosha Judmayer, Nicholas Stifter, Edgar Weippl
A reliable source of randomness is not only an essential building block in various cryptographic, security, and distributed systems protocols, but also plays an integral part in the design of many new blockchain proposals. Consequently, the topic of publicly-verifiable, bias-resistant and unpredictable randomness has recently enjoyed increased attention. In particular random beacon protocols, aimed at continuous operation, can be a vital component for current Proof-of-Stake based distributed ledger proposals. We improve upon previous random beacon approaches with HydRand, a novel distributed protocol based on publicly-verifiable secret sharing (PVSS) to ensure unpredictability, bias-resistance, and public-verifiability of a continuous sequence of random beacon values. Furthermore, HydRand provides guaranteed output delivery of randomness at regular and predictable intervals in the presence of adversarial behavior and does not rely on a trusted dealer for the initial setup. Compared to existing PVSS based approaches that strive to achieve similar properties, our solution improves scalability by lowering the communication complexity from $\mathcal{O}\left( {{n^3}} \right)$ to $\mathcal{O}\left( {{n^2}} \right)$ . Furthermore, we are the first to present a detailed comparison of recently described schemes and protocols that can be used for implementing random beacons.
In this article, we present DPTS, a data payment and transfer the scheme that uses bitcoin payments to reward users for detailed electricity measurements they submit to a utility provider (UP). DPTS emphasizes both privacy and fairness of transactions; not only it allows participants to earn bitcoins in a way that cannot be linked to their actions or identities but also ensures that data are delivered if and only if an appropriate payment is received. While DPTS is described in the smart grid setting, the protocol can also be applied in other areas where incentives are used to increase user participation. One such important area is participatory or crowdsensing, where individuals use their smartphones to report sensed data back to a campaign administrator and obtain a reward for it. DPTS allows users to enjoy the benefits of participation without compromising anonymity. The proposal is coupled with a security analysis showing the privacy-preserving character of the system along with an efficiency analysis demonstrating the feasibility of our approach.
Polkadot is a decentralized blockchain platform to be launched in 2020. It will implement nominated proof-of-stake (NPoS), a proof-of-stake based mechanism where k nodes are selected by the network as validators to participate in the consensus protocol, according to the preferences expressed by token holders who take the role of nominators. This setup leads to an approval-based multi-winner election problem, where each nominator submits a list of trusted candidates, and has a vote strength proportional to their stake. A solution consists of a committee of k validators, together with a fractional distribution of each nominator's vote among them. We consider two objectives, both recently studied in the literature of social choice. The first one is ensuring the property of proportional justified representation (PJR). The second objective, called maximin support, is to maximize the minimum amount of vote support assigned to any elected validator. We argue that the former objective aligns with the notion of decentralization, while the latter aligns with the security level of the consensus protocol.
We prove that the maximin support problem is constant-factor approximable, as we present several approximation algorithms for it, and prove a matching hardness result. Furthermore, we present an efficient post-computation which, when paired with an approximation algorithm for maximin support, returns a new solution that a) preserves the approximation guarantee, b) satisfies the PJR property, and c) can be efficiently verified to satisfy PJR by an untrusting third party. Besides being of independent theoretical interest, our results enable the network to run an efficient validator election protocol that simultaneously achieves the PJR property and a constant-factor approximation for maximin support, thus offering strong theoretical guarantees on decentralization and security.
We propose an autonomous blockchain-based federated learning (BFL) design for privacy-aware and efficient vehicular communication networking, where local on-vehicle machine learning (oVML) model updates are exchanged and verified in a distributed fashion. BFL enables oVML without any centralized training data or coordination by utilizing the consensus mechanism of the blockchain. Relying on a renewal reward approach, we develop a mathematical framework that features the controllable network and BFL parameters (e.g., the retransmission limit, block size, block arrival rate, and the frame sizes) so as to capture their impact on the system-level performance. More importantly, our rigorous analysis of oVML system dynamics quantifies the end-to-end delay with BFL, which provides important insights into deriving optimal block arrival rate by considering communication and consensus delays. We present a variety of numerical and simulation results highlighting various non-trivial findings and insights for adaptive BFL design. In particular, based on analytical results, we minimize the system delay by exploiting the channel dynamics and demonstrate that the proposed idea of tuning the block arrival rate is provably online and capable of driving the system dynamics to the desired operating point. It also identifies the improved dependency on other blockchain parameters for a given set of channel conditions, retransmission limits, and frame sizes.1However, a number of challenges (gaps in knowledge) need to be resolved in order to realise these changes. In particular, we identify key bottleneck challenges requiring further investigations, and provide potential future research directions.1An early version of this work has been accepted for presentation in IEEE WCNC Wksps 2020 [1].
With the rapid development of the Internet of things (IoT), it has brought great convenience for people's life. However, the security and privacy of IoT still face a major challenge. To remedy these issues, in this study, the authors first introduce the three‐tier architecture of IoT and analyse the corresponding security problems of each layer, then they discussed the compatibility between IoT and blockchain. Secondly, they propose a new, distributed blockchain‐based security architecture of IoT, which rely on gateway nodes of perception layer to secure data storage and sharing, and use middleware servers to analyse and process data. Finally, they adopt game theory to model and analyse their designed scheme. The results demonstrate that their scheme is a safe and deployable framework for IoT data security and privacy.
Network provenance is essential for Internet-of-Things (IoT) network administrators to conduct the network diagnostics and identify root causes of network errors. However, the distributed nature of the IoT network results in the management of the provenance data at different trust domains, which poses concerns on the security and trustworthiness of the cross-domain network diagnostics. In this article, we propose a blockchain-based architecture for secure and efficient distributed network provenance (SEDNP) in the IoT. Instead of directly storing and querying the whole provenance data on the blockchain with prohibitive implementation cost, we introduce a unified provenance query model and develop a provenance digest strategy that: 1) enables compact (constant size) on-blockchain digests of provenance data and a multilevel index regardless of provenance data volume and 2) ensures the correctness and integrity of provenance query results through the verification of the on-blockchain digests. We formally define the security requirements as Archiving Security along with thorough security analysis. Moreover, we conduct extensive experiments with the integration of a verifiable computation (VC) framework and a blockchain testing network. The experimental results are provided as performance benchmarks to demonstrate the application feasibility of SEDNP.
The prosperity of cloud computing has driven an increasing number of enterprises and organizations to store their data on private or public cloud platforms. Due to the limitation of individual data owners in terms of data volume and diversity, data sharing over different cloud platforms would enable third parties to take advantage of big data analysis techniques to provide value-added services, such as providing healthcare services for customers by gathering medical data from multiple hospitals. However, it remains a challenging task to design effective incentives that encourage secure and collaborative data sharing in multiple clouds. In this paper, we propose a reliable collaboration model consisting of three types of participants, which include data owners, miners, and third parties, where the data is shared via blockchain and recorded by a smart contract. In general, these participants may acquire and store the sharing of data using their private or public clouds. We analyze the topological relationships between the participants and develop some Shapley value models from simple to complicate in the process of revenue distribution. We also discuss the incentive effect of sharing security data and rationality of the designed solution through analysis towards distribution rules.
Vehicular sensing is advocated to perform data collection by exploiting a plethora of vehicular on-board sensors; meanwhile, with the merging of vehicular sensing and fog computing, the deployed road side units (RSUs) can act as fog nodes to collect and share vehicular sensory data at the network edge. However, there are still several problems in terms of the secure and reliable sharing of sensory data in vehicular fog. To resolve these issues, in this paper, we present an efficient, privacy-preserving and verifiable sensory data collection and sharing scheme with a permissioned blockchain in vehicular fog. During the data collection phase, by combining the homomorphic 2-DNF (Disjunctive Normal Form) cryptosystem and an identity-based signcryption scheme, our proposed scheme achieves the secure and verifiable computation of the average and variance of the collected vehicular sensory data. Meanwhile, to achieve efficient and reliable data sharing, we exploit a permissioned blockchain to maintain an immutable and tamper-proof record of the derived sensory data. Security analysis demonstrates the security properties of the proposed scheme, in terms of location privacy preservation, verifiability and immutability. Performance evaluations are conducted to validate the efficiency of the proposed scheme, i.e., improvements in computation and communication efficiency in comparison with a scheme without exploiting blockchain.
Michał Król, Alberto Sonnino, Argyrios G. Tasiopoulos, Ioannis Psaras · 5 authors
Decentralised cloud computing platforms enable individuals to offer and rent resources in a peer-to-peer fashion. They must assign resources from multiple sellers to multiple buyers and derive prices that match the interests and capacities of both parties. The assignment process must be decentralised, fair and transparent, but also protect the privacy of buyers. We present PASTRAMI, a decentralised platform enabling trustworthy assignments of items and prices between a large number of sellers and bidders, through the support of multi-item auctions. PASTRAMI uses threshold blind signatures and commitment schemes to provide strong privacy guarantees while making bidders accountable. It leverages the Ethereum blockchain for auditability, combining efficient off-chain computations with novel, on-chain proofs of misbehaviour. Our evaluation of PASTRAMI using Filecoin workloads show its ability to efficiently produce trustworthy assignments between thousands of buyers and sellers.
Edge computing, an emerging computing paradigm pushing data computing and storing to network edges, enables many applications that require high computing complexity, scalability, and security. In the big data era, one of the most critical applications is multiparty learning or federated learning, which allows different parties to collaborate with each other to obtain better learning models without sharing their own data. However, there are several main concerns about the current multiparty learning systems. First, most existing systems are distributed and need a central server to coordinate the learning process. However, such a central server can easily become a single point of failure and may not be trustworthy. Second, although quite a few schemes have been proposed to study Byzantine attacks, a very common and challenging kind of attack in distributed systems, they generally consider the scenario of learning a global model. However, in fact, all parties in multiparty learning usually have their own local models. The learning methods and security issues, in this case, are not fully explored. In this article, we propose a novel blockchain-empowered decentralized secure multiparty learning system with heterogeneous local models called BEMA. Particularly, we consider two types of Byzantine attacks, and carefully design “off-chain sample mining” and “on-chain mining ” schemes to protect the security of the proposed system. We theoretically prove the system performance bound and resilience under Byzantine attacks. The simulation results show that the proposed system obtains comparable performance with that of conventional distributed systems, and bounded performance in the case of Byzantine attacks.
In recent years blockchain technology has become mainstream research topic because of its decentralized, peer to peer transaction and anonymity properties. There are several applications of blockchain which are secure and easy as compare to the current techniques. One of the applications is a smart contract. Smart contracts are lines of code which are stored on a blockchain and automatically executed when the conditions defined by the it (developer) are met. This smart contract with the addition of blockchain technology can do task fast and with high security. In this paper we have developed a smart contract for a generalized notary application on solidity, Ethereum and the application is tested using the truffle suite. Furthermore, applications and their methodology for notary applications are also mentioned.
Blockchain-enabled Federated Learning (BFL) enables mobile devices to\ncollaboratively train neural network models required by a Machine Learning\nModel Owner (MLMO) while keeping data on the mobile devices. Then, the model\nupdates are stored in the blockchain in a decentralized and reliable manner.\nHowever, the issue of BFL is that the mobile devices have energy and CPU\nconstraints that may reduce the system lifetime and training efficiency. The\nother issue is that the training latency may increase due to the blockchain\nmining process. To address these issues, the MLMO needs to (i) decide how much\ndata and energy that the mobile devices use for the training and (ii) determine\nthe block generation rate to minimize the system latency, energy consumption,\nand incentive cost while achieving the target accuracy for the model. Under the\nuncertainty of the BFL environment, it is challenging for the MLMO to determine\nthe optimal decisions. We propose to use the Deep Reinforcement Learning (DRL)\nto derive the optimal decisions for the MLMO.\n
Federated learning has been widely studied and applied to various scenarios, such as financial credit, medical identification, and so on. Under these settings, federated learning protects users from exposing their private data, while cooperatively training a shared machine learning algorithm model (i.e., the global model) for a variety of realworld applications. The only data exchanged is the gradient of the model or the updated model (i.e., the local model update). However, the security of federated learning is increasingly being questioned, due to the malicious clients or central servers' constant attack on the global model or user privacy data. To address these security issues, we propose a decentralized federated learning framework based on blockchain, that is, a Block-chain-based Federated Learning framework with Committee consensus (BFLC). Without a centralized server, the framework uses blockchain for the global model storage and the local model update exchange. To enable the proposed BFLC, we also devise an innovative committee consensus mechanism, which can effectively reduce the amount of consensus computing and reduce malicious attacks. We then discuss the scalability of BFLC, including theoretical security, storage optimization, and incentives. Finally, based on a FISCO blockchain system, we perform experiments using an AlexNet model on several frameworks with a real-world dataset FEMNIST. The experimental results demonstrate the effectiveness and security of the BFLC framework.
Fog computing is a new distributed computing paradigm that extends the cloud to the network edge. Fog computing aims at improving quality of service, data access, networking, computation and storage. However, the security and privacy issues persist, even if many cloud solutions were proposed. Indeed, Fog computing introduces new challenges in terms of security and privacy, due to its specific features such as mobility, geo-distribution and heterogeneity etc. Blockchain is an emergent concept bringing efficiency in many fields. In this paper, we propose a new access control scheme based on blockchain technology for the fog computing with fault tolerance in the context of the Internet of Things. Blockchain is used to provide secure management authentication and access process to IoT devices. Each network entity authenticates in the blockchain via the wallet, which allows a secure communication in decentralized environment, hence it achieves the security objectives. In addition, we propose to establish a secure connection between the users and the IoT devices, if their attributes satisfy the policy stored in the blockchain by smart contract. We also address the blockchain transparency problem by the encryption of the users attributes both in the policy and in the request. An authorization token is generated if the encrypted attributes are identical. Moreover, our proposition offers higher scalability, availability and fault tolerance in Fog nodes due to the implementation of load balancing through the Min-Min algorithm.
Personal data are important information assets. Data sharing has potential of creating value to data owners as well as causing security and privacy concerns. Distributed storage solutions have emerged as an approach adhering to the Privacy-by-Design principles and in combination with blockchain technologies enable data and value exchange within communities of Internet users. The paper elaborates an approach for efficient distributed data storage and sharing, where access control is provided using the blockchain technologies and data searching and retrieval are facilitated using a knowledge base. A conceptual model and data management processes are elaborated and a prototype is developed. The prototype is used in experimental studies to compare data storage usage and data retrieval speed for the proposed approach and on-chain storage.
Xun Yi, Russell Paulet, Elisa Bertino, Fang-Yu Rao
In this paper we consider the problem where a client wishes to subscribe to some product or service provided by a server, but maintain their anonymity. At the same time, the server must be able to authenticate the client as a genuine user and be able to discontinue (or revoke) the client's access if the subscription fees are not paid. Current solutions for this problem are typically constructed using some combination of blind signature or zero-knowledge proof techniques, which do not directly support client revocation (that is, revoking a user before expiry of their secret value). In this paper, we present a solution for this problem on the basis of the broadcast encryption scheme, suggested by Boneh et al., by which the server can broadcast a secret to a group of legitimate clients. Our solution allows the registered client to log into the server anonymously and also supports client revocation by the server. Our solution can be used in many applications, such as location-based queries. We formally define a model for our anonymous subscription protocol and prove the security of our solution under this model. In addition, we present experimental results from an implementation of our protocol. These experimental results demonstrate that our protocol is practical.
With the development of precise positioning technology, a growing number of location-based services (LBS) emerge. For example, visit a specific place to get the corresponding reward. This also leads to location fraud by illegal users in order to gain benefits. Thus, it is necessary to verify location certificates provided by users. However, present proof of location systems are deficient in verifying users’ location certificates while protecting users’ privacy. Users do not flexibly control their location certificates either. Based on blockchain, a kind of distributed proof of location system architecture was proposed and based on the proposed system architecture, a kind of proof of location protocol with zero-knowledge proof was proposed further. With the proposed architecture and the protocol, the proposed proof of location system allows users to freely select disclosed certificate parameters and positional accuracy according to their needs so that hierarchical location privacy protection was achieved.
By exploiting the massive data generated from the numerous interconnected machines and control systems, industrial Internet-of-Things (IIoT) provides unprecedented opportunities for facilitating the intelligence and smartness of manufacturing. Timely processing the large-scaled IIoT data by the conventional computation framework, such as Cloud computing, however, is nontrivial due to its costly resource usage, intolerable delay, and unbearable backbone pressures. By leveraging the idle resources of smart objects at the edge, mobile device cloud (MDC) becomes promising for the IIoT data analysis, thanks to the flexible resource provision and nearby task offloading. However, MDC workers are mostly human-carried devices with large scale, high dynamic resource provision, and untruthful behaviors, which pose significant challenges on MDC task allocation. In this article, we propose a blockchain-based decentralized and truthful framework for MDC (BC-MDC). BC-MDC enables the decentralization and prevents dishonesty by incorporating a plasma-based blockchain into the MDC. We design four smart contracts for distributedly managing the worker registration, task posting/allocation, rewarding, and penalizing. Furthermore, MDC task allocation is formulated as a stochastic optimization problem that jointly minimizes the long-term processing cost and risk of task failing. We also design a truthful reward/penalty algorithm that stimulates workers to provide resources and enforce them to keep the promise as well. Collaborated by the extensive simulation tests, we show how our proposed scheme achieves low cost on usage and high truthfulness and outperforms state-of-the-art solutions.