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Blockchain, like any other complex technology, needs a strong testing methodology to support its evolution in both research and development contexts. Setting up meaningful tests for permissionless blockchain technology is a notoriously complex task for several reasons: software is complex, a large number of nodes are involved, the network is non-ideal, etc. Developers usually adopt small virtual laboratories or costly real devnets based on real software. Researchers usually prefer simulations of a large number of nodes based on simplified models.In this paper, we aim to obtain the advantages of both approaches, i.e., performing large, realistic, inexpensive, and flexible experiments, using real blockchain software within a virtual environment. To do that, we address the challenge of running large blockchain networks in a single physical machine, leveraging Linux and Docker. We analyze a number of problems that arise when large blockchain networks are emulated, and we provide technical solutions for all of them. Finally, we describe two experiences of emulating fairly large blockchain networks on a single machine: adopting both research-oriented and production-oriented software and involving more than 3000 containers.

Proving that an endpoint (e.g. URL, telephone number, etc.) is controlled by a subject is crucial in many applications. In the web, this is witnessed by the widespread adoption of HTTPS. In centralized architectures, this task is usually carried out by trusted certification authorities (CAs). In decentralized applications, for example based on blockchains, or for self-sovereign identity management (SSI), it would be desirable to perform these checks in a decentralized way, relying on the collective behavior of a society of individuals rather than on a single trusted entity. In any case, the result should be a widely usable certificate, as in the centralized CA case. In this paper, we show two blockchain-based methods to prove the association between a subject and an endpoint in a decentralized manner. Our methods are compatible with a wide variety of endpoints and contribute to fill the gap of the current SSI approaches with respect to decentralization. We analyze the security of our proposal and provide a proof-of-concept implementation. We also evaluate performances, costs, and compatibility with current standardization efforts about SSI.

Commercial off-the-shelf DataBase Management Systems (DBMSes) are highly optimized to process a wide range of queries by means of carefully designed indexing and query planning. However, many aggregate range queries are usually performed by DBMSes using sequential scans, and certain needs, like storing Authenticated Data Structures (ADS), are not supported at all. Theoretically, these needs could be efficiently fulfilled adopting specific kinds of indexing, which however are normally ruled-out in DBMSes design. We introduce the concept of overlay index: an index that is meant to be stored in a standard database, alongside regular data and managed by regular software, to complement DBMS capabilities. We show a data structure, that we call DB-tree, that realizes an overlay index to support a wide range of custom aggregate range queries as well as ADSes, efficiently. All DB-trees operations can be performed by executing a small number of queries to the DBMS, that can be issued in parallel in one or two query rounds, and involves a logarithmic amount of data. We experimentally evaluate the efficiency of DB-trees showing that our approach is effective, especially if data updates are limited.

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.