The Internet of Things is a paradigm that is becom- ing more and more implemented in a wide variety of devices that communicate between themselves. Under the form of a Machine- to-Machine (M2M) communication, it is integrated by a highly heterogeneous community where many devices are constrained in resources, being yet transmitting sensible data. Therefore, it is necessary to guarantee that the M2M communication is equally safer that traditional networks, in which the HTTP Secure (HTTPS) protocol is used. With this aim, we propose in this paper the implementation of the Constrained Application Protocol (CoAP) together with the Datagram Transport Secure Layer (DTLS), all based on the Contiki operating system, this last being a very popular development platform for WSNs. Additionally, we present an analysis of the threats that occur in the previously described communication environments in order to identify key elements in...