Centralized entities, such as cloud services, message brokers or Public Key Infrastructure (PKI), pose a problem for the trustworthiness of Internet of Things (IoT) services, as they take up a central role in establishment of communication as well as data storage and therefore hide the internal data processing from the users. At the same time they are an attractive target for attackers to steal, manipulate or expose data captured by IoT devices. This thesis approaches the stated problem with the development of a messaging framework based on the decentralized Blockchain technology. Blockchains distribute the task of data storage among the nodes of a network and ensure that state transitions are only executed when the majority of network nodes endorse them, i.e., reaching consensus. As a result of this decentralization, full transparency of the stored data is given and there is no longer a single target for attackers. The proposed Decentralized IoT Framework (DIoT) differs from existing general-purpose Blockchain solutions as it is designed to incorporate existing devices of an IoT network, such as single-board computers or network gateways, as full Blockchain nodes and can therefore operate without the need of external mining infrastructure and transaction fees and still provide transparent and manipulationresistant data storage and communication to IoT networks. Apart from the design and implementation of the DIoT framework, a series of experiments are conducted to evaluate functional and non-functional aspects of a DIoT Blockchain in execution.
