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Abstract
Internet of Things (IoT) comprises millions of everyday devices which are connected and exchange information through the Internet. However, IoT security and privacy remains a major challenge due to the ever increasing number of IoT devices, their heterogeneity and the highly personal nature of the data that they collect from our urban surroundings. In recent years, blockchain has attracted tremendous attention as a means to address security and privacy concerns in IoT due to its salient features including auditability, immutability, and decentralization. However, conventional blockchains are computationally expensive, have limited scalability and incur significant bandwidth and memory overheads and delays, making them unsuitable for IoT ecosystems.
This thesis makes three novel contributions. We first propose a Lightweight Scalable blockchain (LSB) that achieves decentralization by forming an overlay network where high resource devices jointly manage the blockchain. To increase scalability, the overlay nodes are organized into clusters and only the cluster heads manage the blockchain by storing and verifying new transactions and blocks. We propose a Distributed Time-based Consensus algorithm (DTC) which reduces the mining processing overhead and delay. A distributed trust approach is employed by the cluster heads to progressively reduce the processing overhead for verifying new blocks. LSB also incorporates a Distributed Throughput Management (DTM) algorithm which ensures that the blockchain throughput does not significantly deviate from the cumulative transaction load in the network. Qualitative arguments demonstrate that our approach is resilient to several security attacks. Extensive simulations show that packet overhead and delay are decreased compared to relevant baselines.
Next, we propose a Memory Optimized and Flexible Blockchain (MOF-BC) that enables IoT users and service providers to remove or summarize their transactions and thus reduce the blockchain memory footprint. We propose MOF-BC as a generalized solution, which can be implemented on top of any existing or future blockchain instantiation. A flexible transaction fee model and a reward mechanism is proposed to incentivize users to participate in optimizing memory consumption. MOF-BC introduces the notion of a Generator Verifier (GV) which is a signed hash of a Generator Verifier Secret (GVS) which enables the IoT users to manage their transactions with a single key. The GV changes for each transaction to provide privacy yet is signed by a unique key, thus minimizing the information that needs to be stored. Qualitative security and privacy analysis demonstrates that MOF-BC is resilient against several security attacks. Evaluation results show that MOF-BC decreases BC memory consumption by up to 25% and the cost incurred by users by more than two orders of magnitude compared to conventional blockchain instantiations.
Blockchain is increasingly being used to provide a distributed, secure, trusted, and private framework for energy trading. However, existing solutions suffer from lack of privacy, processing and packet overheads, and reliance on Trusted Third Parties (TTP) to secure the trade. To address these challenges, we propose a Secure Private Blockchain-based (SPB) framework as our last contribution. SPB proposes a routing method which routes packets based on the destination Public Key (PK) to reduce the packet overhead for negotiating energy price. SPB eliminates the reliance on TTP to ensure both energy producer and consumer commit to their obligations by introducing atomic meta-transactions. In the latter, a constitute transaction is considered to be valid only if it is coupled with one other transaction. SPB introduces a private authentication method to increase the anonymity of the users. We benchmark SPB's performance against the relevant state-of-the-art. The implementation results demonstrate that SPB incurs lower overheads and monetary cost for end users to trade energy compared to existing solutions.