Recently, blockchain-based IoT solutions have been proposed that address
trust limitation by maintaining data consistency, immutability, and
chronology in IoT environments. However, IoT ecosystems are
resource-constrained and have low bandwidth and finite computing power
of sensor nodes. Thus, the inclusion of blockchain requires an effective
policy design regarding consensus and smart contract environments in
heterogeneous IoT applications. Recent studies have presented blockchain
as a potential solution in IoT, but an effective view of consensus and
smart contract design to meet the end application requirements is an
open problem. Motivated by the same, the survey presents the integration
of suitable low-powered consensus protocols and smart contract design to
assess and validate the blockchain-IoT ecosystems. We discuss the key
blockchain concepts and present the scalability and performance issues
of consensus protocols to support IoT. Further, we discuss smart
contract vulnerabilities and blockchain attacks. Open issues and future
directions are presented, supported through a case study of low-powered
consensus protocol design in the blockchain- IoT ecosystem. The survey
intends to drive novel solutions for future consensus and safe, smart
contract designs to support applicative IoT ecosyst