Numerous blockchain simulators have been proposed to allow researchers to simulate mainstream blockchains. However, we have not yet found a testbed that enables researchers to develop and evaluate their new consensus algorithms or new protocols for blockchain sharding systems. To fill this gap, we developed BlockEmulator, which is designed as an experimental platform, particularly for emulating blockchain sharding mechanisms. BlockEmulator adopts a lightweight blockchain architecture so developers can only focus on implementing their new protocols or mechanisms. Using layered modules and useful programming interfaces offered by BlockEmulator, researchers can implement a new protocol with minimum effort. Through experiments, we test various functionalities of BlockEmulator in two steps. Firstly, we prove the correctness of the emulation results yielded by BlockEmulator by comparing the theoretical analysis with the observed experiment results. Secondly, other experimental results demonstrate that BlockEmulator can facilitate measuring a series of metrics, including throughput, transaction confirmation latency, cross-shard transaction ratio, the queuing status of transaction pools, workload distribution across blockchain shards, etc. We have made BlockEmulator open-source in Github.

Economic systems play pivotal roles in the metaverse. However, we have not yet found an overview that systematically introduces economic systems for the metaverse. Therefore, we review the state-of-the-art solutions, architectures, and systems related to economic systems. When investigating those state-of-the-art studies, we keep two questions in mind: (1) What is the framework of economic systems in the context of the metaverse? and (2) What activities would economic systems engage in the metaverse? This article aims to disclose insights into the economic systems that work for both the current and the future metaverse. To have a clear overview of the economic system framework, we mainly discuss the connections among three fundamental elements in the metaverse, i.e., digital creation, digital assets, and the digital trading market. After that, we elaborate on each topic of the proposed economic system framework. Those topics include incentive mechanisms, monetary systems, digital wallets, decentralized finance activities, and cross-platform interoperability for the metaverse. For each topic, we mainly discuss three questions: (a) the rationale of this topic, (b) why the metaverse needs this topic, and (c) how this topic will evolve in the metaverse. Through this overview, we wish readers can better understand what economic systems the metaverse needs and the insights behind the economic activities in the metaverse.

With the popularity of the mobile Internet, data is increasingly becoming a new resource. Therefore, the trading of such data resources has become an increasing demand. In this paper, we propose a fair privacy-preserving data trading protocol based on blockchain. Firstly, our data trading protocol achieves fairness by carefully combining the probabilistic approaches and the fully homomorphic encryption techniques. Moreover, our protocol allows online arbitration when misbehavior occurs in the trading process is detected. Note that previous data trading protocols need a Trusted Third Party (TTP) or an offline arbitrator to solve disputes, weakening the trust of those protocols. Secondly, the data validity verification process of our protocol is more flexible. Most Importantly, different from all previous designs which only achieve privacy against communication channel eavesdroppers, our protocol achieves privacy against any eavesdropper and the passive arbitrator. The above-distinguishing properties of our protocol are mainly benefited from the homomorphic encryption and double encryption techniques. In addition, our data trading protocol can be instantiated with post-quantum primitives and thus achieves post-quantum security. To demonstrate the feasibility of the proposed protocol, we conduct a comprehensive evaluation with the instantiated cryptographic primitives based on the Ethereum test network.

With the application of blockchain in Internet of Things (IoT), various IoT scenario-oriented blockchains have been proposed, meaning that multichain future within IoT ecosystem is growing. Cross-chain interoperability thus is essential. Sidechains is one of the crucial technologies for cross-chain interoperability, which allows blockchains to interoperate with each other. However, sidechains encounters practicability challenges impeding adoption, such as poor generality and inefficiency. In this article, we propose practical and secure sidechain construction (PSSC)in the form of parent-child chains, a practical and secure sidechains construction for heterogeneous blockchains orienting IoT scenarios. To achieve practicability, we first utilize succinct noninteractive argument of knowledge (SNARK), which is succinct noninteractive proof (arguments) of knowledge, to reproduce the state transition of blockchains, so that PSSC can get rid of the constraints on consensus mechanisms of blockchains; we then design an impawn-punish mechanism based on smart contract, which transfers the work verifying SNARK proof from mainchain to sidechain, preventing fork threat to mainchain. Due to employing SNARK based on recursive proof composition to generate cross-chain proof, our PSSC is more efficient with succinct cross-chain proof, reducing the overhead of storage of nodes. Besides, we formally prove our PSSC satisfies the three fundamental security properties of sidechains: 1) persistence; 2) liveness; and 3) firewall. Finally, we develop a proof-of-concept implementation of PSSC, and the experimental results show that the proof size of PSSC is about 28.8 kB, which is roughly $2094\times $ , $9.36\times $ , $6.56\times $ , $4.23\times $ , and $3.27\times $ smaller than BTCRelay proof, PoW sidechains proof, PoS sidechains, zkRelay proof, and fast sidechains, respectively.

Metaverse brings unlimited space and tremendous potential since it is an integrated application of multiple fundamental technologies such as artificial intelligence, blockchain, networking, Internet of Things, and interactivity. During those building blocks of metaverse, blockchain is a type of technology operated by a group of individual participants and known for its immutability feature. The massive adoption of blockchain has been severely prevented by various security and scalability issues in blockchain-based applications due to the inherent characteristics of this technology. To accelerate the massive adoption of blockchain, many previous studies have been carried out to address the security and scalability issues. This article reviews blockchain-related publications collected from four major security conferences (i.e., NDSS, CCS, S&P, and USENIX Security) published in the past three years. Through this overview, we disclose the security and scalability issues of mainstream blockchains such as Bitcoin and Ethereum. Our study aims to help researchers better understand the bottleneck of blockchain-empowered metaverse, and how to address user requirements for security and scalability from the perspective of blockchains.

Efficient and secure data sharing in the Internet of Vehicles (IoV) is critical for the advancement of intelligent transportation, particularly in the context of emerging 5G/6G networks and driverless technology. This has prompted researchers to explore Blockchain-based Internet of Vehicles (BIoV) solutions to address common issues in intelligent transportation systems (ITS). However, at the edge layer, existing reputation and consensus mechanisms in the BIoV model face challenges such as significant energy consumption, limited scalability, and pronounced centralization. To tackle these issues, we introduce TRCO, a Permissioned Blockchain-based Trusted and Robust Consensus Optimization orienting ITS. TRCO is a three-layer BIoV architecture applicable to any BIoV scenario, offering robust scalability with the addition of new sub-regions. To improve the quality of data sharing for edge layer, we propose a decentralized reputation evaluation mechanism and integrate PoS and PBFT consensus algorithms to enhance performance by evaluating the communication behavior of edge servers. Security analysis and simulation experiments demonstrate that TRCO achieves high scalability and reliability, effectively filters Byzantine edge servers, and enhances the decentralization and consensus efficiency of the system.