Blockchain has received tremendous attention as a secure, distributed, and anonymous framework for the Internet of Things (IoT). As a distributed system, blockchain trades off scalability for distribution, which limits the technologys adaptation for large scale networks such as IoT. All transactions and blocks must be broadcast and verified by all participants which limits scalability and incurs computational and communication overheads. The existing solutions to scale blockchains have so far led to partial recentralization, limiting the technologys original appeal. In this paper, we introduce a distributed yet scalable Verification and Communication architecture for blockchain referred to as Vericom. Vericom concurrently achieves high scalability and distribution using hash function outputs to shift blockchains from broadcast to multicast communication. Unlike conventional blockchains where all nodes must verify new transactions/blocks, Vericom uses the hash of IoT traffic to randomly select a set of nodes to verify transactions/blocks which in turn reduces the processing overhead. Vericom incorporates two layers: i) transmission layer where a randomized multicasting method is introduced along with a backbone network to route traffic, i.e., transactions and blocks, from the source to the destination, and ii) verification layer where a set of randomly selected nodes are allocated to verify each transaction or block. The performance evaluation shows that Vericom reduces the packet and processing overhead as compared with conventional blockchains. In the worst case, packet overhead in Vericom scales linearly with the number of nodes while the processing overhead remains scale-independent.
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