  The Internet of Things (IoT) is transforming our physical world into a
complex and dynamic system of connected devices on an unprecedented scale.
Connecting everyday physical objects is creating new business models, improving
processes and reducing costs and risks. Recently, blockchain technology has
received a lot of attention from the community as a possible solution to
overcome security issues in IoT. However, traditional blockchains (such as the
ones used in Bitcoin and Ethereum) are not well suited to the
resource-constrained nature of IoT devices and also with the large volume of
information that is expected to be generated from typical IoT deployments. To
overcome these issues, several researchers have presented lightweight instances
of blockchains tailored for IoT. For example, proposing novel data structures
based on blocks with decoupled and appendable data. However, these researchers
did not discuss how the consensus algorithm would impact their solutions, i.e.,
the decision of which consensus algorithm would be better suited was left as an
open issue. In this paper, we improved an appendable-block blockchain framework
to support different consensus algorithms through a modular design. We
evaluated the performance of this improved version in different emulated
scenarios and studied the impact of varying the number of devices and
transactions and employing different consensus algorithms. Even adopting
different consensus algorithms, results indicate that the latency to append a
new block is less than 161ms (in the more demanding scenario) and the delay for
processing a new transaction is less than 7ms, suggesting that our improved
version of the appendable-block blockchain is efficient and scalable, and thus
well suited for IoT scenarios.
