Soutenance de thèse de Julio Perez-Garcia – 18 décembre 2023

Titre : Contribution to security and privacy in the Blockchain-based Internet of Things: Robustness, Reliability, and Scalability.

Résumé : The Internet of Things (IoT) is a diverse network of objects or ”things” typically interconnected via the Internet. Given the sensitivity of the information exchanged in IoT applications, it is essential to guarantee security and privacy. This problem is aggravated by the open nature of wireless communications, and the power and computing resource limitations of most IoT devices. At the same time, existing IoT security solutions are based on centralized architectures, which raises scalability issues and the single point of failure problem, making them susceptible to denial-of-service attacks and technical failures. Blockchain has emerged as an attractive solution to IoT security and centralization issues. Blockchains replicate a permanent, append-only record of all transactions occurring on a network across multiple devices, keeping them synchronized through a consensus protocol. Blockchain implementation may involve high computational and energy costs for devices. Consequently, solutions based on Fog/Edge computing have been considered in the integration with IoT. This approach shifts the higher computational load and higher energy consumption to the devices with higher resource availability, i.e., Fog/Edge devices. However, the cost of Blockchain utilization must be optimized, especially in the consensus protocol, which significantly influences the overall system performance. Permissioned Blockchains align better with the requirements of IoT applications than Permissionless Blockchains, due to their high transaction processing rate and scalability. This is because the consensus nodes, i.e., Validators, are known and predetermined. In existing consensus protocols used in Permissioned Blockchains, the Validators are usually a predefined or randomly selected set of nodes, which affects both system performance and fairness among users. The objective of this work is to propose solutions to improve security and privacy within IoT by integrating Blockchain technology, as well as to maximize fairness levels during consensus. The study is organized into two distinct parts: one addresses critical aspects of IoT security and proposes Blockchain-based solutions, while the other part focuses on optimizing fairness among users during the execution of the consensus algorithm on the Blockchain. We present an authentication mechanism inspired by the μTesla authentication protocol, which uses symmetric keys that form a hashchain and achieves asymmetric properties by unveiling the key used a while later. With this mechanism and the use of the Blockchain to store the keys and facilitate authentication, our proposal ensures robust and efficient authentication of devices, without the need for a trusted third party. In addition, we introduce a Blockchain-based key management system for group communications adapted to IoT contexts. The use of Elliptic Curve Cryptography ensures a low computational cost while enabling secure distribution of group keys. In both security solutions, we provide formal and informal proofs of security under the defined attack model. A performance impact analysis and a comparison with existing solutions are also conducted for the proposed solutions, showing that the proposed solutions are secure and efficient and can be used in multiple IoT applications. The second part of the work proposes an algorithm to select Validator nodes in Permissioned Blockchains maximizing Social Welfare, using α-Fairness as the objective function. A mathematical model of the problem is developed, and a method for finding the solution in a distributed manner is proposed, employing metaheuristic Evolutionary algorithms and a Search-space partitioning strategy. The security of the proposed algorithm and the quality of the solutions obtained are analyzed. As a result of this work, two security protocols for IoT based on Blockchain are introduced, along with a distributed algorithm for maximizing Social Welfare among users in a Permissioned Blockchain network.