In recent years, Blockchain has attracted tremendous attention due to its salient features including auditability, immutability, security, and anonymity. Resulting from these salient features, blockchain has been applied in multiple non-monetary applications including the Internet of Things (IoT). However, blockchain is computationally expensive, has limited scalability and incurs significant bandwidth overheads and delays which are not suited for most IoT applications. In this paper, we propose a Lightweight Scalable blockchain (LSB) that is optimized for IoT requirements while also providing end-to-end security. Our blockchain instantiation achieves decentralization by forming an overlay network where high resource devices jointly manage the blockchain. The overlay is organized as distinct clusters to reduce overheads and the cluster heads are responsible for managing the public blockchain. We propose a Distributed Time-based Consensus algorithm (DTC) which reduces the mining processing overhead and delay. Distributed trust approach is employed by the cluster heads to progressively reduce the processing overhead for verifying new blocks. LSB 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. We explore our approach in a smart home setting as a representative example for broader IoT applications. Qualitative arguments demonstrate that our approach is resilient to several security attacks. Extensive simulations show that packet overhead and delay are decreased and blockchain scalability is increased compared to relevant baselines.
