  With the rapid development of wireless sensor networks, smart devices, and
traditional information and communication technologies, there is tremendous
growth in the use of Internet of Things (IoT) applications and services in our
everyday life. IoT systems deal with high volumes of data. This data can be
particularly sensitive, as it may include health, financial, location, and
other highly personal information. Fine-grained security management in IoT
demands effective access control. Several proposals discuss access control for
the IoT, however, a limited focus is given to the emerging blockchain-based
solutions for IoT access control. In this paper, we review the recent trends
and critical needs for blockchain-based solutions for IoT access control. We
identify several important aspects of blockchain, including decentralised
control, secure storage and sharing information in a trustless manner, for IoT
access control including their benefits and limitations. Finally, we note some
future research directions on how to converge blockchain in IoT access control
efficiently and effectively.
