  The Internet of Things brings new ways to collect privacy-sensitive data from
billions of devices. Well-tailored distributed ledger technologies (DLTs) can
provide high transaction processing capacities to IoT devices in a
decentralized fashion. However, privacy aspects are often neglected or
unsatisfying, with a focus mainly on performance and security. In this paper,
we introduce decentralized usage control mechanisms to empower IoT devices to
control the data they generate. Usage control defines obligations, i.e.,
actions to be fulfilled to be granted access, and conditions on the system in
addition to data dissemination control. The originality of this paper is to
consider the usage control system as a component of distributed ledger
networks, instead of an external tool. With this integration, both technologies
work in synergy, benefiting their privacy, security and performance. We
evaluated the performance improvements of integration using the IOTA
technology, particularly suitable due to the participation of small devices in
the consensus. The results of the tests on a private network show an
approximate 90% decrease of the time needed for the UCS to push a transaction
and make its access decision in the integrated setting, regardless of the
number of nodes in the network.
