  Blockchain and distributed ledger technologies have received significant
interest in various areas beyond the financial sector, with profound
applications in the Internet of Things (IoT), providing the means for creating
truly trustless and secure solutions for IoT applications. Taking into account
the weak security defences that the majority of IoT devices have, it is
critical that a blockchain-based solution targeting the IoT is not only capable
of addressing the many challenges IoT is facing, but also does not introduce
other defects, in terms of performance, making its adoption hard to achieve.
This paper aims at addressing the above needs by providing a comprehensive and
coherent review of the available blockchain solutions to determine their
ability to meet the requirements and tackle the challenges of the IoT, using
the smart home as the reference domain. Key architectural aspects of blockchain
solutions are examined in terms of their ability to withstand various types of
common IoT and blockchain attacks, deliver enhanced privacy features, and
assure adequate performance levels while processing large amounts of
transactions being generated in an IoT environment. The analysis carried out
identified that the defences currently provided by blockchain platforms are not
sufficient to thwart all the prominent attacks against blockchains, with
blockchain 1.0 and 2.0 platforms being susceptible to the majority of them. On
the other side, privacy related mechanisms are being supported, to varying
degrees, by all platforms investigated; however, each of the them tackles
specific only privacy aspects, thus rendering the overall privacy evaluation a
challenging task which needs to be considered in an ad-hoc basis. If the
underlying consensus protocols performance and fault tolerance is also
considered, then only a small number of platforms meet the requirements of our
reference IoT domain.
