The Internet of Things (IoT) is experiencing exponential growth in research and industry, but
it still suffers from privacy and security vulnerabilities. Conventional security and privacy
approaches tend to be inapplicable for IoT, mainly due to its decentralized topology and the
resource-constraints of the majority of its devices. BlockChain (BC) that underpin the cryptocurrency
Bitcoin have been recently used to provide security and privacy in peer-to-peer
networks with similar topologies to IoT. However, BCs are computationally expensive and
involve high bandwidth overhead and delays, which are not suitable for IoT devices. This
position paper proposes a new secure, private, and lightweight architecture for IoT, based on
BC technology that eliminates the overhead of BC while maintaining most of its security and
privacy benefits. The described method is investigated on a smart home application as a
representative case study for broader IoT applications. The proposed architecture is
hierarchical, and consists of smart homes, an overlay network and cloud storages
coordinating data transactions with BC to provide privacy and security. Our design uses
different types of BC’s depending on where in the network hierarchy a transaction occurs,
and uses distributed trust methods to ensure a decentralized topology. Qualitative evaluation
of the architecture under common threat models highlights its effectiveness in providing
security and privacy for IoT applications.