  The world has been experiencing a mind-blowing expansion of blockchain
technology since it was first introduced as an emerging means of cryptocurrency
called bitcoin. Currently, it has been regarded as a pervasive frame of
reference across almost all research domains, ranging from virtual cash to
agriculture or even supply-chain to the Internet of Things. The ability to have
a self-administering register with legitimate immutability makes blockchain
appealing for the Internet of Things (IoT). As billions of IoT devices are now
online in distributed fashion, the huge challenges and questions require to
addressed in pursuit of urgently needed solutions. The present paper has been
motivated by the aim of facilitating such efforts. The contribution of this
work is to figure out those trade-offs the IoT ecosystem usually encounters
because of the wrong choice of blockchain technology. Unlike a survey or
review, the critical findings of this paper target sorting out specific
security challenges of blockchain-IoT Infrastructure. The contribution includes
how to direct developers and researchers in this domain to pick out the
unblemished combinations of Blockchain enabled IoT applications. In addition,
the paper promises to bring a deep insight on Ethereum, Hyperledger blockchain
and IOTA technology to show their limitations and prospects in terms of
performance and scalability.
