When IoT devices operate not only with the owner of the device but also with third parties, identifying the device using a permanent identifier, e.g., a hardware identifier, can present privacy problems due to the identifier facilitating tracking and correlation attacks. A changeable identifier can be used to reduce the risk on privacy. This paper looks at using decentralised identifiers (DIDs), an upcoming standard of self-sovereign identifiers with multiple competing implementations, with IoT devices. The paper analyses the resource requirements of running DIDs on the IoT devices and finds that even quite small devices can successfully deploy DIDs and proposes that the most constrained devices could rely on a proxy approach. Finally, the privacy benefits and limitations of using DIDs are analysed, with the conclusion that DIDs significantly improve the users’ privacy when utilised properly.

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There has been increased interest in the use of blockchains to control Internet of Things devices either directly, or through smart contracts. Many blockchains, such as Ethereum and Fabric, have support for smart contracts. The use of public blockchains while attractive due to their decentralization and availability, do pose challenges, such as unpredictable transaction latencies and cryptocurrency price fluctuations. Transactions in the Ethereum network, such as invokations of smart contracts used to control an IoT device, have no fairness or eventuality guarantees. In this work we describe a "spam attack" method available to parties with sufficient cryptocurrency reserves to delay a statistically significant portion of transactions submitted to the Ethereum network. This paper derives estimations on the costs and effects of such an attack, and is based on an analysis of historical transactions.

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