Public blockchains should be able to scale with respect to the number of nodes and to the transactions workload. The blockchain scalability trilemma has been informally conjectured. This is related to scalability, security and decentralization, stating that any improvement in one of these aspects should negatively impact on at least one of the other twos. In fact, despite the large research and experimental effort, all known approaches turn out to be tradeoffs.We theoretically describe a new blockchain architecture that scales to arbitrarily high workload provided that a corresponding proportional increment of nodes is provisioned. We show that, under reasonable assumptions, our approach does not require tradeoffs on security or decentralization. To the best of our knowledge, this is the first result that disprove the trilemma considering the scalability of all architectural elements of a blockchain and not only the consensus protocol. While our result is currently only theoretic, we believe that our approach may stimulate significant practical contributions.

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.

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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.