  Blockchain has come to provide transparency, reliability as well as to
increase the security in computer systems, especially in distributed ones like
the Internet of Things (IoT). A few integrations have been proposed in this
context so far; however, most of these solutions do not pay special attention
to the interoperability of the IoT, one of the biggest challenges in this
field. In this paper, a Blockchain solution has been integrated into the OMA
Lightweight M2M (LwM2M), a promising industry IoT protocol for global
interoperability. This integration provides reliability and auditability to the
LwM2M protocol enabling IoT devices (LwM2M clients) to transparently interact
with the protocol. Furthermore, a missing reliable API to allow users and
applications to securely interact with the system and an interface to store
critical information like anomalies for auditability have been defined.
