  The Internet of Things (IoT) necessitates robust access control mechanisms to
secure a vast array of interconnected devices. Most of the existing IoT systems
in practice use centralized solutions. We identify the problems in such
solutions and adopt the blockchain based decentralized access control approach.
Though there are works in the literature that use blockchain for access
control, there are some gaps in these works. We develop a blockchain embedded
access control (BEAC) framework to bridge the gaps. First, blockchain based
solutions for access control require an enabling P2P network while existing P2P
overlays do not support some required features. We develop a novel P2P
infrastructure to seamlessly support our BEAC framework. Second, most of the
works consider blockchain based access control for a single access control
model, and we develop a generic blockchain mechanism and show that it can
support the embedding of various access control models. Finally, existing works
adopt existing blockchain mechanisms which may incur a high communication
overhead. We develop a shortcut approach to improve the number of message
rounds in the access protocol. Our experiments demonstrate the efficacy of our
system, showing that the shortcut mechanism can reduces access time by
approximately 43%.
