  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.
