Flying Ad hoc Network (FANET) has drawn significant consideration due to its rapid advancements and extensive use in civil applications. However, the characteristics of FANET including high mobility, limited resources, and distributed nature, have posed a new challenge to develop a secure and efficient routing scheme for FANET. To overcome these challenges, this paper proposes a novel cluster based secure routing scheme, which aims to solve the routing and data security problem of FANET. In this scheme, the optimal cluster head selection is based on residual energy, online time, reputation, blockchain transactions, mobility, and connectivity by using Improved Artificial Bee Colony Optimization (IABC). The proposed IABC utilizes two different search equations for employee bee and onlooker bee to enhance convergence rate and exploitation abilities. Further, a lightweight blockchain consensus algorithm, AI-Proof of Witness Consensus Algorithm (AI-PoWCA) is proposed, which utilizes the optimal cluster head for mining. In AI-PoWCA, the concept of the witness for block verification is also involved to make the proposed scheme resource efficient and highly resilient against 51% attack. Simulation results demonstrate that the proposed scheme outperforms its counterparts and achieves up to 90% packet delivery ratio, lowest end-to-end delay, highest throughput, resilience against security attacks, and superior in block processing time.

Layer 2 solutions have emerged in recent years as a valuable alternative to increase the throughput and scalability of blockchain-based architectures. The three primary types of Layer 2 solutions are state channels, sidechains, and rollups. The rollups are particularly promising, allowing significant improvements in transaction throughput, security, and efficiency, and have been adopted by many real-world projects, such as Polygon and Optimistic. However, the adoption of Layer 2 solutions has led to other challenges, such as the data availability problem, where transaction data processed off-chain must be posted back on the main chain. This is crucial to prevent data withholding attacks and ensure all participants can independently verify the blockchain state. This paper provides a comprehensive survey of existing rollup-based Layer 2 solutions with a focus on the data availability problem and discusses the major advantages and disadvantages of them. Finally, an analysis of open challenges and future research directions is provided.

Blockchain technology has been successfully applied in recent years to promote the immutability, traceability, and authenticity of previously collected and stored data. However, the amount of data stored in the blockchain is usually limited for economic and technological issues. Namely, the blockchain usually stores only a fingerprint of data, such as the hash of data, while full, raw information is stored off-chain. This is generally enough to guarantee immutability and traceability, but misses to support another important property, that is, data availability. This is particularly true when a traditional, centralized database is chosen for off-chain storage. For this reason, many proposals try to properly combine blockchain with decentralized IPFS storage. However, the storage of data on IPFS could pose some privacy problems. This paper proposes a solution that properly combines blockchain, IPFS, and encryption techniques to guarantee immutability, traceability, availability, and data privacy.

The recent spread of smart contracts in several application domains presents challenges in scalability, efficiency, management, and security. In this regard, some design patterns have been proposed to factorize common parts, prevent replicated deployment by promoting reusability, and apply some role-based access control (RBAC) techniques during smart contract execution. In particular, the factory pattern has been widely recognized as a common practice to solve the scalability issue, reducing also the increased gas costs related to both smart contract deployment and its subsequent use. However, in real-world applications, the factory pattern can be considered too limited since it only allows the instantiation of a single type or family of contracts. On the other side, no solutions have been proposed that tightly integrate a factory pattern with RBAC functionalities. In this paper, we propose an extension of the factory pattern, called the hierarchical factory pattern, which integrates a multirole authentication and authorization mechanism tailored explicitly to this pattern since it allows a secure, efficient, and role-specific interaction between the various layers of the hierarchy. The paper ends with some considerations about performance and scalability.

Layer 2 (L2) solutions have recently been developed with the aim of increasing scalability and throughput of traditional blockchain networks such as Bitcoin and Ethereum. The main idea of L2 is to move expensive computations out of the main (L1) network and post back only a summary of the performed transactions. This allows L2 solutions to inherit the security and trustworthiness of L1 while reducing computation and transaction costs. However, data availability, namely the possibility for all blockchain participants to access the data processed outside L1 to verify state transitions independently, is a challenge in L2 solutions. Namely, while on-chain data availability approaches suffer from high costs and long waiting times, off-chain approaches can pose data security risks. This paper takes into consideration the recent introduction of the blob data structure and proposes an Adaptive Multi-Factor Scoring (AMFS) to efficiently manage blobs while dynamically optimizing cost and waiting time. The proposed solution ensures low waiting times and blob posting costs, particularly for small rollups, by implementing the concept of shared blob, maintaining security without compromising performance.

Blockchain technology and smart contracts have recently emerged as valid tools for implementing applications dealing with data due to their ability to provide immutability, traceability, and availability properties. However, in recent years, applications dealing with data need to comply with some data protection regulations, such as the GDPR in Europe. These regulations typically specify a set of rights for data subjects, like the right to be forgotten or the right to rectification, that are apparently in contrast with the blockchain properties mentioned above. This paper investigates how the eight data subject rights prescribed by the GDPR could be supported by a proper combination of blockchain, smart contracts, and encryption techniques. The discussion will proceed in an incremental way by describing how increased support for the GDPR rights requires increased sophistication of the provided solution.