Internet of things networks have spread to most digital applications in the
past years. Examples of these networks include smart home networks, wireless
sensor networks, Internet of Flying Things, and many others. One of the main
difficulties that confront these networks is the security of their information
and communications. A large number of solutions have been proposed to safeguard
these networks from various types of cyberattacks. Among these solutions is the
blockchain, which gained popularity in the last few years due to its strong
security characteristics, such as immutability, cryptography, and distributed
consensus. However, implementing the blockchain framework within the devices of
these networks is very challenging, due to the limited resources of these
devices and the resource-demanding requirements of the blockchain. For this
reason, a large number of researchers proposed various types of lightweight
blockchain solutions for resource-constrained networks. The "lightweight"
aspect can be related to the blockchain architecture, device authentication,
cryptography model, consensus algorithm, or storage method. In this paper, we
present a taxonomy of the lightweight blockchain solutions that have been
proposed in the literature and discuss the different methods that have been
applied so far in each "lightweight" category. Our review highlights the
missing points in existing systems and paves the way to building a complete
lightweight blockchain solution for resource-constrained networks.Comment: 64 pages, 11 figures