In the IoT-based economy, a large number of subjects (companies, public bodies, or private citizens) are willing to buy data or services offered by subjects that provide, operate, or host IoT devices. To support economic transactions in this setting, and to pave the way for the implementation of decentralized algorithmic governance powered by smart contracts, the adoption of the blockchain has been proposed both in scientific literature and in actual projects. The blockchain technology promises a decentralized payment system independent of (and possibly cheaper than) conventional electronic payment systems. However, there are a number of aspects that need to be considered for an effective IoT–blockchain integration. In this review paper, we start from a number of real IoT projects and applications that (may) take advantage of blockchain technology to support economic transactions. We provide a reasoned review of several architectural choices in light of typical requirements of those applications and discuss their impact on transaction throughput, latency, costs, limits on ecosystem growth, and so on. We also provide a survey of additional financial tools that a blockchain can potentially bring to an IoT ecosystem, with their architectural impact. In the end, we observe that there are very few examples of IoT projects that fully exploit the potential of the blockchain. We conclude with a discussion of open problems and future research directions to make blockchain adoption easier and more effective for supporting an IoT economy.

Smart cities leverage Information and Communication Technologies (ICTs) to enhance the quality of urban services. However, it is nowadays clear that the success of a smart city largely depends on the level of engagement of its citizens. In this paper we explore to what extent disruptive blockchain technologies can be used to incentivise the democratic participation of citizen. The investigated approach extends the standard IoT cycle 1) sense data, 2) cloudify and elaborate them, and 3) push information to the users. Here, the user takes an active role by means of data-informed votes on policies, therefore influencing behaviours. We illustrate such an approach by means of a proof-of-concept decentralised application (dApp) supporting the negotiation of polices for the management of urban water resources. The dApp consists of a smart contract that manages the execution of other smart contracts (the policies) according to the data-driven choices of the community. This use case demonstrates how suitably blockchain technologies can support fair and safe access to data and user engagement in smart cities.

In many applications, identity management (IdM) is used to associate a subject public key with an endpoint at which the subject can be contacted (telephone number, email, etc.). In decentralized applications based on distributed ledger technologies (DLTes), it is desirable for the IdM to be decentralized as well. Currently, endpoints are either verified by who needs it, which is impractical in DLT-based applications, or by a centralized authority, which contrasts with the spirit of DLTes.In this paper, we show two DLT-based protocols to prove the association between a subject and an endpoint in a decentralized manner, contributing in filling the gap of the current IdM approaches with respect to decentralization. Our protocols are compatible with a wide variety of endpoints. We analyze the security of our protocols and evaluate their performance and cost against the common approaches.

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